Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

Pull virtio updates from Michael Tsirkin: - A new virtio RTC driver - vhost scsi now logs write descriptors so migration works - Some hardening work in virtio core - An old spec compliance issue fixed in vhost net - A couple of cleanups, fixes in vringh, virtio-pci, vdpa * tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost: virtio: reject shm region if length is zero virtio_rtc: Add RTC class driver virtio_rtc: Add Arm Generic Timer cross-timestamping virtio_rtc: Add PTP clocks virtio_rtc: Add module and driver core vringh: use bvec_kmap_local vhost: vringh: Use matching allocation type in resize_iovec() virtio-pci: Fix result size returned for the admin command completion vdpa/octeon_ep: Control PCI dev enabling manually vhost-scsi: log event queue write descriptors vhost-scsi: log control queue write descriptors vhost-scsi: log I/O queue write descriptors vhost-scsi: adjust vhost_scsi_get_desc() to log vring descriptors vhost: modify vhost_log_write() for broader users
2025-12-27 11:06:41 -05:00 · 2025-05-29 08:15:35 -07:00
parent 43db111107 206cc44588
commit 8ca154e491
15 changed files with 2707 additions and 36 deletions
--- a/7
+++ b/7
@@ -26073,6 +26073,13 @@ S:	Maintained
 F:	drivers/nvdimm/nd_virtio.c
 F:	drivers/nvdimm/virtio_pmem.c

+VIRTIO RTC DRIVER
+M:	Peter Hilber <quic_philber@quicinc.com>
+L:	virtualization@lists.linux.dev
+S:	Maintained
+F:	drivers/virtio/virtio_rtc_*
+F:	include/uapi/linux/virtio_rtc.h
+
 VIRTIO SOUND DRIVER
 M:	Anton Yakovlev <anton.yakovlev@opensynergy.com>
 M:	"Michael S. Tsirkin" <mst@redhat.com>
--- a/drivers/vdpa/octeon_ep/octep_vdpa_main.c
+++ b/drivers/vdpa/octeon_ep/octep_vdpa_main.c
@@ -454,6 +454,9 @@ static void octep_vdpa_remove_pf(struct pci_dev *pdev)
 		octep_iounmap_region(pdev, octpf->base, OCTEP_HW_MBOX_BAR);

 	octep_vdpa_pf_bar_expand(octpf);
+
+	/* The pf version does not use managed PCI. */
+	pci_disable_device(pdev);
 }

 static void octep_vdpa_vf_bar_shrink(struct pci_dev *pdev)
@@ -825,7 +828,7 @@ static int octep_vdpa_probe_pf(struct pci_dev *pdev)
 	struct octep_pf *octpf;
 	int ret;

-	ret = pcim_enable_device(pdev);
+	ret = pci_enable_device(pdev);
 	if (ret) {
 		dev_err(dev, "Failed to enable device\n");
 		return ret;
@@ -834,15 +837,17 @@ static int octep_vdpa_probe_pf(struct pci_dev *pdev)
 	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64));
 	if (ret) {
 		dev_err(dev, "No usable DMA configuration\n");
-		return ret;
+		goto disable_pci;
 	}
 	octpf = devm_kzalloc(dev, sizeof(*octpf), GFP_KERNEL);
-	if (!octpf)
-		return -ENOMEM;
+	if (!octpf) {
+		ret = -ENOMEM;
+		goto disable_pci;
+	}

 	ret = octep_iomap_region(pdev, octpf->base, OCTEP_HW_MBOX_BAR);
 	if (ret)
-		return ret;
+		goto disable_pci;

 	pci_set_master(pdev);
 	pci_set_drvdata(pdev, octpf);
@@ -856,6 +861,8 @@ static int octep_vdpa_probe_pf(struct pci_dev *pdev)

 unmap_region:
 	octep_iounmap_region(pdev, octpf->base, OCTEP_HW_MBOX_BAR);
+disable_pci:
+	pci_disable_device(pdev);
 	return ret;
 }

--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -133,6 +133,11 @@ struct vhost_scsi_cmd {
 	struct se_cmd tvc_se_cmd;
 	/* Sense buffer that will be mapped into outgoing status */
 	unsigned char tvc_sense_buf[TRANSPORT_SENSE_BUFFER];
+	/*
+	 * Dirty write descriptors of this command.
+	 */
+	struct vhost_log *tvc_log;
+	unsigned int tvc_log_num;
 	/* Completed commands list, serviced from vhost worker thread */
 	struct llist_node tvc_completion_list;
 	/* Used to track inflight cmd */
@@ -258,6 +263,12 @@ struct vhost_scsi_tmf {
 	struct iovec resp_iov;
 	int in_iovs;
 	int vq_desc;
+
+	/*
+	 * Dirty write descriptors of this command.
+	 */
+	struct vhost_log *tmf_log;
+	unsigned int tmf_log_num;
 };

 /*
@@ -362,6 +373,45 @@ static int vhost_scsi_check_prot_fabric_only(struct se_portal_group *se_tpg)
 	return tpg->tv_fabric_prot_type;
 }

+static int vhost_scsi_copy_cmd_log(struct vhost_virtqueue *vq,
+				   struct vhost_scsi_cmd *cmd,
+				   struct vhost_log *log,
+				   unsigned int log_num)
+{
+	if (!cmd->tvc_log)
+		cmd->tvc_log = kmalloc_array(vq->dev->iov_limit,
+					     sizeof(*cmd->tvc_log),
+					     GFP_KERNEL);
+
+	if (unlikely(!cmd->tvc_log)) {
+		vq_err(vq, "Failed to alloc tvc_log\n");
+		return -ENOMEM;
+	}
+
+	memcpy(cmd->tvc_log, log, sizeof(*cmd->tvc_log) * log_num);
+	cmd->tvc_log_num = log_num;
+
+	return 0;
+}
+
+static void vhost_scsi_log_write(struct vhost_virtqueue *vq,
+				 struct vhost_log *log,
+				 unsigned int log_num)
+{
+	if (likely(!vhost_has_feature(vq, VHOST_F_LOG_ALL)))
+		return;
+
+	if (likely(!log_num || !log))
+		return;
+
+	/*
+	 * vhost-scsi doesn't support VIRTIO_F_ACCESS_PLATFORM.
+	 * No requirement for vq->iotlb case.
+	 */
+	WARN_ON_ONCE(unlikely(vq->iotlb));
+	vhost_log_write(vq, log, log_num, U64_MAX, NULL, 0);
+}
+
 static void vhost_scsi_release_cmd_res(struct se_cmd *se_cmd)
 {
 	struct vhost_scsi_cmd *tv_cmd = container_of(se_cmd,
@@ -408,6 +458,10 @@ static void vhost_scsi_release_tmf_res(struct vhost_scsi_tmf *tmf)
 {
 	struct vhost_scsi_inflight *inflight = tmf->inflight;

+	/*
+	 * tmf->tmf_log is default NULL unless VHOST_F_LOG_ALL is set.
+	 */
+	kfree(tmf->tmf_log);
 	kfree(tmf);
 	vhost_scsi_put_inflight(inflight);
 }
@@ -517,6 +571,8 @@ vhost_scsi_do_evt_work(struct vhost_scsi *vs, struct vhost_scsi_evt *evt)
 	struct vhost_virtqueue *vq = &vs->vqs[VHOST_SCSI_VQ_EVT].vq;
 	struct virtio_scsi_event *event = &evt->event;
 	struct virtio_scsi_event __user *eventp;
+	struct vhost_log *vq_log;
+	unsigned int log_num;
 	unsigned out, in;
 	int head, ret;

@@ -527,9 +583,19 @@ vhost_scsi_do_evt_work(struct vhost_scsi *vs, struct vhost_scsi_evt *evt)

 again:
 	vhost_disable_notify(&vs->dev, vq);
+
+	vq_log = unlikely(vhost_has_feature(vq, VHOST_F_LOG_ALL)) ?
+		vq->log : NULL;
+
+	/*
+	 * Reset 'log_num' since vhost_get_vq_desc() may reset it only
+	 * after certain condition checks.
+	 */
+	log_num = 0;
+
 	head = vhost_get_vq_desc(vq, vq->iov,
 			ARRAY_SIZE(vq->iov), &out, &in,
-			NULL, NULL);
+			vq_log, &log_num);
 	if (head < 0) {
 		vs->vs_events_missed = true;
 		return;
@@ -559,6 +625,8 @@ vhost_scsi_do_evt_work(struct vhost_scsi *vs, struct vhost_scsi_evt *evt)
 		vhost_add_used_and_signal(&vs->dev, vq, head, 0);
 	else
 		vq_err(vq, "Faulted on vhost_scsi_send_event\n");
+
+	vhost_scsi_log_write(vq, vq_log, log_num);
 }

 static void vhost_scsi_complete_events(struct vhost_scsi *vs, bool drop)
@@ -660,6 +728,9 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
 		} else
 			pr_err("Faulted on virtio_scsi_cmd_resp\n");

+		vhost_scsi_log_write(cmd->tvc_vq, cmd->tvc_log,
+				     cmd->tvc_log_num);
+
 		vhost_scsi_release_cmd_res(se_cmd);
 	}

@@ -676,6 +747,7 @@ vhost_scsi_get_cmd(struct vhost_virtqueue *vq, u64 scsi_tag)
 					struct vhost_scsi_virtqueue, vq);
 	struct vhost_scsi_cmd *cmd;
 	struct scatterlist *sgl, *prot_sgl;
+	struct vhost_log *log;
 	int tag;

 	tag = sbitmap_get(&svq->scsi_tags);
@@ -687,9 +759,11 @@ vhost_scsi_get_cmd(struct vhost_virtqueue *vq, u64 scsi_tag)
 	cmd = &svq->scsi_cmds[tag];
 	sgl = cmd->sgl;
 	prot_sgl = cmd->prot_sgl;
+	log = cmd->tvc_log;
 	memset(cmd, 0, sizeof(*cmd));
 	cmd->sgl = sgl;
 	cmd->prot_sgl = prot_sgl;
+	cmd->tvc_log = log;
 	cmd->tvc_se_cmd.map_tag = tag;
 	cmd->inflight = vhost_scsi_get_inflight(vq);

@@ -1063,13 +1137,17 @@ vhost_scsi_send_bad_target(struct vhost_scsi *vs,

 static int
 vhost_scsi_get_desc(struct vhost_scsi *vs, struct vhost_virtqueue *vq,
-		    struct vhost_scsi_ctx *vc)
+		    struct vhost_scsi_ctx *vc,
+		    struct vhost_log *log, unsigned int *log_num)
 {
 	int ret = -ENXIO;

+	if (likely(log_num))
+		*log_num = 0;
+
 	vc->head = vhost_get_vq_desc(vq, vq->iov,
 				     ARRAY_SIZE(vq->iov), &vc->out, &vc->in,
-				     NULL, NULL);
+				     log, log_num);

 	pr_debug("vhost_get_vq_desc: head: %d, out: %u in: %u\n",
 		 vc->head, vc->out, vc->in);
@@ -1221,6 +1299,8 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 	u8 task_attr;
 	bool t10_pi = vhost_has_feature(vq, VIRTIO_SCSI_F_T10_PI);
 	u8 *cdb;
+	struct vhost_log *vq_log;
+	unsigned int log_num;

 	mutex_lock(&vq->mutex);
 	/*
@@ -1236,8 +1316,11 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)

 	vhost_disable_notify(&vs->dev, vq);

+	vq_log = unlikely(vhost_has_feature(vq, VHOST_F_LOG_ALL)) ?
+		vq->log : NULL;
+
 	do {
-		ret = vhost_scsi_get_desc(vs, vq, &vc);
+		ret = vhost_scsi_get_desc(vs, vq, &vc, vq_log, &log_num);
 		if (ret)
 			goto err;

@@ -1386,6 +1469,14 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 			goto err;
 		}

+		if (unlikely(vq_log && log_num)) {
+			ret = vhost_scsi_copy_cmd_log(vq, cmd, vq_log, log_num);
+			if (unlikely(ret)) {
+				vhost_scsi_release_cmd_res(&cmd->tvc_se_cmd);
+				goto err;
+			}
+		}
+
 		pr_debug("vhost_scsi got command opcode: %#02x, lun: %d\n",
 			 cdb[0], lun);
 		pr_debug("cmd: %p exp_data_len: %d, prot_bytes: %d data_direction:"
@@ -1421,11 +1512,14 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 		 */
 		if (ret == -ENXIO)
 			break;
-		else if (ret == -EIO)
+		else if (ret == -EIO) {
 			vhost_scsi_send_bad_target(vs, vq, &vc, TYPE_IO_CMD);
-		else if (ret == -ENOMEM)
+			vhost_scsi_log_write(vq, vq_log, log_num);
+		} else if (ret == -ENOMEM) {
 			vhost_scsi_send_status(vs, vq, &vc,
 					       SAM_STAT_TASK_SET_FULL);
+			vhost_scsi_log_write(vq, vq_log, log_num);
+		}
 	} while (likely(!vhost_exceeds_weight(vq, ++c, 0)));
 out:
 	mutex_unlock(&vq->mutex);
@@ -1467,6 +1561,8 @@ static void vhost_scsi_tmf_resp_work(struct vhost_work *work)
 	mutex_lock(&tmf->svq->vq.mutex);
 	vhost_scsi_send_tmf_resp(tmf->vhost, &tmf->svq->vq, tmf->in_iovs,
 				 tmf->vq_desc, &tmf->resp_iov, resp_code);
+	vhost_scsi_log_write(&tmf->svq->vq, tmf->tmf_log,
+			     tmf->tmf_log_num);
 	mutex_unlock(&tmf->svq->vq.mutex);

 	vhost_scsi_release_tmf_res(tmf);
@@ -1490,7 +1586,8 @@ static void
 vhost_scsi_handle_tmf(struct vhost_scsi *vs, struct vhost_scsi_tpg *tpg,
 		      struct vhost_virtqueue *vq,
 		      struct virtio_scsi_ctrl_tmf_req *vtmf,
-		      struct vhost_scsi_ctx *vc)
+		      struct vhost_scsi_ctx *vc,
+		      struct vhost_log *log, unsigned int log_num)
 {
 	struct vhost_scsi_virtqueue *svq = container_of(vq,
 					struct vhost_scsi_virtqueue, vq);
@@ -1518,6 +1615,19 @@ vhost_scsi_handle_tmf(struct vhost_scsi *vs, struct vhost_scsi_tpg *tpg,
 	tmf->in_iovs = vc->in;
 	tmf->inflight = vhost_scsi_get_inflight(vq);

+	if (unlikely(log && log_num)) {
+		tmf->tmf_log = kmalloc_array(log_num, sizeof(*tmf->tmf_log),
+					     GFP_KERNEL);
+		if (tmf->tmf_log) {
+			memcpy(tmf->tmf_log, log, sizeof(*tmf->tmf_log) * log_num);
+			tmf->tmf_log_num = log_num;
+		} else {
+			pr_err("vhost_scsi tmf log allocation error\n");
+			vhost_scsi_release_tmf_res(tmf);
+			goto send_reject;
+		}
+	}
+
 	if (target_submit_tmr(&tmf->se_cmd, tpg->tpg_nexus->tvn_se_sess, NULL,
 			      vhost_buf_to_lun(vtmf->lun), NULL,
 			      TMR_LUN_RESET, GFP_KERNEL, 0,
@@ -1531,6 +1641,7 @@ vhost_scsi_handle_tmf(struct vhost_scsi *vs, struct vhost_scsi_tpg *tpg,
 send_reject:
 	vhost_scsi_send_tmf_resp(vs, vq, vc->in, vc->head, &vq->iov[vc->out],
 				 VIRTIO_SCSI_S_FUNCTION_REJECTED);
+	vhost_scsi_log_write(vq, log, log_num);
 }

 static void
@@ -1567,6 +1678,8 @@ vhost_scsi_ctl_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 	struct vhost_scsi_ctx vc;
 	size_t typ_size;
 	int ret, c = 0;
+	struct vhost_log *vq_log;
+	unsigned int log_num;

 	mutex_lock(&vq->mutex);
 	/*
@@ -1580,8 +1693,11 @@ vhost_scsi_ctl_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)

 	vhost_disable_notify(&vs->dev, vq);

+	vq_log = unlikely(vhost_has_feature(vq, VHOST_F_LOG_ALL)) ?
+		vq->log : NULL;
+
 	do {
-		ret = vhost_scsi_get_desc(vs, vq, &vc);
+		ret = vhost_scsi_get_desc(vs, vq, &vc, vq_log, &log_num);
 		if (ret)
 			goto err;

@@ -1645,9 +1761,12 @@ vhost_scsi_ctl_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 			goto err;

 		if (v_req.type == VIRTIO_SCSI_T_TMF)
-			vhost_scsi_handle_tmf(vs, tpg, vq, &v_req.tmf, &vc);
-		else
+			vhost_scsi_handle_tmf(vs, tpg, vq, &v_req.tmf, &vc,
+					      vq_log, log_num);
+		else {
 			vhost_scsi_send_an_resp(vs, vq, &vc);
+			vhost_scsi_log_write(vq, vq_log, log_num);
+		}
 err:
 		/*
 		 * ENXIO:  No more requests, or read error, wait for next kick
@@ -1657,11 +1776,13 @@ vhost_scsi_ctl_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 		 */
 		if (ret == -ENXIO)
 			break;
-		else if (ret == -EIO)
+		else if (ret == -EIO) {
 			vhost_scsi_send_bad_target(vs, vq, &vc,
 						   v_req.type == VIRTIO_SCSI_T_TMF ?
 						   TYPE_CTRL_TMF :
 						   TYPE_CTRL_AN);
+			vhost_scsi_log_write(vq, vq_log, log_num);
+		}
 	} while (likely(!vhost_exceeds_weight(vq, ++c, 0)));
 out:
 	mutex_unlock(&vq->mutex);
@@ -1756,6 +1877,24 @@ static void vhost_scsi_flush(struct vhost_scsi *vs)
 		wait_for_completion(&vs->old_inflight[i]->comp);
 }

+static void vhost_scsi_destroy_vq_log(struct vhost_virtqueue *vq)
+{
+	struct vhost_scsi_virtqueue *svq = container_of(vq,
+					struct vhost_scsi_virtqueue, vq);
+	struct vhost_scsi_cmd *tv_cmd;
+	unsigned int i;
+
+	if (!svq->scsi_cmds)
+		return;
+
+	for (i = 0; i < svq->max_cmds; i++) {
+		tv_cmd = &svq->scsi_cmds[i];
+		kfree(tv_cmd->tvc_log);
+		tv_cmd->tvc_log = NULL;
+		tv_cmd->tvc_log_num = 0;
+	}
+}
+
 static void vhost_scsi_destroy_vq_cmds(struct vhost_virtqueue *vq)
 {
 	struct vhost_scsi_virtqueue *svq = container_of(vq,
@@ -1775,6 +1914,7 @@ static void vhost_scsi_destroy_vq_cmds(struct vhost_virtqueue *vq)

 	sbitmap_free(&svq->scsi_tags);
 	kfree(svq->upages);
+	vhost_scsi_destroy_vq_log(vq);
 	kfree(svq->scsi_cmds);
 	svq->scsi_cmds = NULL;
 }
@@ -2084,6 +2224,7 @@ vhost_scsi_clear_endpoint(struct vhost_scsi *vs,
 static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
 {
 	struct vhost_virtqueue *vq;
+	bool is_log, was_log;
 	int i;

 	if (features & ~VHOST_SCSI_FEATURES)
@@ -2096,12 +2237,39 @@ static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
 		return -EFAULT;
 	}

+	if (!vs->dev.nvqs)
+		goto out;
+
+	is_log = features & (1 << VHOST_F_LOG_ALL);
+	/*
+	 * All VQs should have same feature.
+	 */
+	was_log = vhost_has_feature(&vs->vqs[0].vq, VHOST_F_LOG_ALL);
+
 	for (i = 0; i < vs->dev.nvqs; i++) {
 		vq = &vs->vqs[i].vq;
 		mutex_lock(&vq->mutex);
 		vq->acked_features = features;
 		mutex_unlock(&vq->mutex);
 	}
+
+	/*
+	 * If VHOST_F_LOG_ALL is removed, free tvc_log after
+	 * vq->acked_features is committed.
+	 */
+	if (!is_log && was_log) {
+		for (i = VHOST_SCSI_VQ_IO; i < vs->dev.nvqs; i++) {
+			if (!vs->vqs[i].scsi_cmds)
+				continue;
+
+			vq = &vs->vqs[i].vq;
+			mutex_lock(&vq->mutex);
+			vhost_scsi_destroy_vq_log(vq);
+			mutex_unlock(&vq->mutex);
+		}
+	}
+
+out:
 	mutex_unlock(&vs->dev.mutex);
 	return 0;
 }
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2304,6 +2304,19 @@ static int log_used(struct vhost_virtqueue *vq, u64 used_offset, u64 len)
 	return 0;
 }

+/*
+ * vhost_log_write() - Log in dirty page bitmap
+ * @vq:      vhost virtqueue.
+ * @log:     Array of dirty memory in GPA.
+ * @log_num: Size of vhost_log arrary.
+ * @len:     The total length of memory buffer to log in the dirty bitmap.
+ *	     Some drivers may only partially use pages shared via the last
+ *	     vring descriptor (i.e. vhost-net RX buffer).
+ *	     Use (len == U64_MAX) to indicate the driver would log all
+ *           pages of vring descriptors.
+ * @iov:     Array of dirty memory in HVA.
+ * @count:   Size of iovec array.
+ */
 int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
 		    unsigned int log_num, u64 len, struct iovec *iov, int count)
 {
@@ -2327,15 +2340,14 @@ int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
 		r = log_write(vq->log_base, log[i].addr, l);
 		if (r < 0)
 			return r;
-		len -= l;
-		if (!len) {
-			if (vq->log_ctx)
-				eventfd_signal(vq->log_ctx);
-			return 0;
-		}
+
+		if (len != U64_MAX)
+			len -= l;
 	}
-	/* Length written exceeds what we have stored. This is a bug. */
-	BUG();
+
+	if (vq->log_ctx)
+		eventfd_signal(vq->log_ctx);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(vhost_log_write);
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -225,10 +225,9 @@ static int resize_iovec(struct vringh_kiov *iov, gfp_t gfp)

 	flag = (iov->max_num & VRINGH_IOV_ALLOCATED);
 	if (flag)
-		new = krealloc_array(iov->iov, new_num,
-				     sizeof(struct iovec), gfp);
+		new = krealloc_array(iov->iov, new_num, sizeof(*new), gfp);
 	else {
-		new = kmalloc_array(new_num, sizeof(struct iovec), gfp);
+		new = kmalloc_array(new_num, sizeof(*new), gfp);
 		if (new) {
 			memcpy(new, iov->iov,
 			       iov->max_num * sizeof(struct iovec));
@@ -1291,11 +1290,10 @@ static inline int getu16_iotlb(const struct vringh *vrh,
 		if (ret)
 			return ret;
 	} else {
-		void *kaddr = kmap_local_page(ivec.iov.bvec[0].bv_page);
-		void *from = kaddr + ivec.iov.bvec[0].bv_offset;
+		__virtio16 *from = bvec_kmap_local(&ivec.iov.bvec[0]);

-		tmp = READ_ONCE(*(__virtio16 *)from);
-		kunmap_local(kaddr);
+		tmp = READ_ONCE(*from);
+		kunmap_local(from);
 	}

 	*val = vringh16_to_cpu(vrh, tmp);
@@ -1330,11 +1328,10 @@ static inline int putu16_iotlb(const struct vringh *vrh,
 		if (ret)
 			return ret;
 	} else {
-		void *kaddr = kmap_local_page(ivec.iov.bvec[0].bv_page);
-		void *to = kaddr + ivec.iov.bvec[0].bv_offset;
+		__virtio16 *to = bvec_kmap_local(&ivec.iov.bvec[0]);

-		WRITE_ONCE(*(__virtio16 *)to, tmp);
-		kunmap_local(kaddr);
+		WRITE_ONCE(*to, tmp);
+		kunmap_local(to);
 	}

 	return 0;
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -188,4 +188,68 @@ config VIRTIO_DEBUG

 	  If unsure, say N.

+config VIRTIO_RTC
+	tristate "Virtio RTC driver"
+	depends on VIRTIO
+	depends on PTP_1588_CLOCK_OPTIONAL
+	help
+	 This driver provides current time from a Virtio RTC device. The driver
+	 provides the time through one or more clocks. The Virtio RTC PTP
+	 clocks and/or the Real Time Clock driver for Virtio RTC must be
+	 enabled to expose the clocks to userspace.
+
+	 To compile this code as a module, choose M here: the module will be
+	 called virtio_rtc.
+
+	 If unsure, say M.
+
+if VIRTIO_RTC
+
+comment "WARNING: Consider enabling VIRTIO_RTC_PTP and/or VIRTIO_RTC_CLASS."
+	depends on !VIRTIO_RTC_PTP && !VIRTIO_RTC_CLASS
+
+comment "Enable PTP_1588_CLOCK in order to enable VIRTIO_RTC_PTP."
+	depends on PTP_1588_CLOCK=n
+
+config VIRTIO_RTC_PTP
+	bool "Virtio RTC PTP clocks"
+	default y
+	depends on PTP_1588_CLOCK
+	help
+	 This exposes any Virtio RTC clocks as PTP Hardware Clocks (PHCs) to
+	 userspace. The PHC sysfs attribute "clock_name" describes the clock
+	 type.
+
+	 If unsure, say Y.
+
+config VIRTIO_RTC_ARM
+	bool "Virtio RTC cross-timestamping using Arm Generic Timer"
+	default y
+	depends on VIRTIO_RTC_PTP && ARM_ARCH_TIMER
+	help
+	 This enables Virtio RTC cross-timestamping using the Arm Generic Timer.
+	 It only has an effect if the Virtio RTC device also supports this. The
+	 cross-timestamp is available through the PTP clock driver precise
+	 cross-timestamp ioctl (PTP_SYS_OFFSET_PRECISE2 aka
+	 PTP_SYS_OFFSET_PRECISE).
+
+	 If unsure, say Y.
+
+comment "Enable RTC_CLASS in order to enable VIRTIO_RTC_CLASS."
+	depends on RTC_CLASS=n
+
+config VIRTIO_RTC_CLASS
+	bool "Real Time Clock driver for Virtio RTC"
+	default y
+	depends on RTC_CLASS
+	help
+	 This exposes the Virtio RTC UTC-like clock as a Linux Real Time Clock.
+	 It only has an effect if the Virtio RTC device has a UTC-like clock
+	 which smears leap seconds to avoid steps. The Real Time Clock is
+	 read-only, and may support setting an alarm.
+
+	 If unsure, say Y.
+
+endif # VIRTIO_RTC
+
 endif # VIRTIO_MENU
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -14,3 +14,8 @@ obj-$(CONFIG_VIRTIO_VDPA) += virtio_vdpa.o
 obj-$(CONFIG_VIRTIO_MEM) += virtio_mem.o
 obj-$(CONFIG_VIRTIO_DMA_SHARED_BUFFER) += virtio_dma_buf.o
 obj-$(CONFIG_VIRTIO_DEBUG) += virtio_debug.o
+obj-$(CONFIG_VIRTIO_RTC) += virtio_rtc.o
+virtio_rtc-y := virtio_rtc_driver.o
+virtio_rtc-$(CONFIG_VIRTIO_RTC_PTP) += virtio_rtc_ptp.o
+virtio_rtc-$(CONFIG_VIRTIO_RTC_ARM) += virtio_rtc_arm.o
+virtio_rtc-$(CONFIG_VIRTIO_RTC_CLASS) += virtio_rtc_class.o
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -48,6 +48,7 @@ void vp_modern_avq_done(struct virtqueue *vq)
 {
 	struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev);
 	struct virtio_pci_admin_vq *admin_vq = &vp_dev->admin_vq;
+	unsigned int status_size = sizeof(struct virtio_admin_cmd_status);
 	struct virtio_admin_cmd *cmd;
 	unsigned long flags;
 	unsigned int len;
@@ -56,7 +57,17 @@ void vp_modern_avq_done(struct virtqueue *vq)
 	do {
 		virtqueue_disable_cb(vq);
 		while ((cmd = virtqueue_get_buf(vq, &len))) {
-			cmd->result_sg_size = len;
+			/* If the number of bytes written by the device is less
+			 * than the size of struct virtio_admin_cmd_status, the
+			 * remaining status bytes will remain zero-initialized,
+			 * since the buffer was zeroed during allocation.
+			 * In this case, set the size of command_specific_result
+			 * to 0.
+			 */
+			if (len < status_size)
+				cmd->result_sg_size = 0;
+			else
+				cmd->result_sg_size = len - status_size;
 			complete(&cmd->completion);
 		}
 	} while (!virtqueue_enable_cb(vq));
--- a/drivers/virtio/virtio_rtc_arm.c
+++ b/drivers/virtio/virtio_rtc_arm.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Provides cross-timestamp params for Arm.
+ *
+ * Copyright (C) 2022-2023 OpenSynergy GmbH
+ * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/clocksource_ids.h>
+
+#include <uapi/linux/virtio_rtc.h>
+
+#include "virtio_rtc_internal.h"
+
+/* see header for doc */
+
+int viortc_hw_xtstamp_params(u8 *hw_counter, enum clocksource_ids *cs_id)
+{
+	*hw_counter = VIRTIO_RTC_COUNTER_ARM_VCT;
+	*cs_id = CSID_ARM_ARCH_COUNTER;
+
+	return 0;
+}
--- a/drivers/virtio/virtio_rtc_class.c
+++ b/drivers/virtio/virtio_rtc_class.c
@@ -0,0 +1,262 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * virtio_rtc RTC class driver
+ *
+ * Copyright (C) 2023 OpenSynergy GmbH
+ * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/math64.h>
+#include <linux/overflow.h>
+#include <linux/rtc.h>
+#include <linux/time64.h>
+
+#include <uapi/linux/virtio_rtc.h>
+
+#include "virtio_rtc_internal.h"
+
+/**
+ * struct viortc_class - RTC class wrapper
+ * @viortc: virtio_rtc device data
+ * @rtc: RTC device
+ * @vio_clk_id: virtio_rtc clock id
+ * @stopped: Whether RTC ops are disallowed. Access protected by rtc_lock().
+ */
+struct viortc_class {
+	struct viortc_dev *viortc;
+	struct rtc_device *rtc;
+	u16 vio_clk_id;
+	bool stopped;
+};
+
+/**
+ * viortc_class_get_locked() - get RTC class wrapper, if ops allowed
+ * @dev: virtio device
+ *
+ * Gets the RTC class wrapper from the virtio device, if it is available and
+ * ops are allowed.
+ *
+ * Context: Caller must hold rtc_lock().
+ * Return: RTC class wrapper if available and ops allowed, ERR_PTR otherwise.
+ */
+static struct viortc_class *viortc_class_get_locked(struct device *dev)
+{
+	struct viortc_class *viortc_class;
+
+	viortc_class = viortc_class_from_dev(dev);
+	if (IS_ERR(viortc_class))
+		return viortc_class;
+
+	if (viortc_class->stopped)
+		return ERR_PTR(-EBUSY);
+
+	return viortc_class;
+}
+
+/**
+ * viortc_class_read_time() - RTC class op read_time
+ * @dev: virtio device
+ * @tm: read time
+ *
+ * Context: Process context.
+ * Return: Zero on success, negative error code otherwise.
+ */
+static int viortc_class_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct viortc_class *viortc_class;
+	time64_t sec;
+	int ret;
+	u64 ns;
+
+	viortc_class = viortc_class_get_locked(dev);
+	if (IS_ERR(viortc_class))
+		return PTR_ERR(viortc_class);
+
+	ret = viortc_read(viortc_class->viortc, viortc_class->vio_clk_id, &ns);
+	if (ret)
+		return ret;
+
+	sec = div_u64(ns, NSEC_PER_SEC);
+
+	rtc_time64_to_tm(sec, tm);
+
+	return 0;
+}
+
+/**
+ * viortc_class_read_alarm() - RTC class op read_alarm
+ * @dev: virtio device
+ * @alrm: alarm read out
+ *
+ * Context: Process context.
+ * Return: Zero on success, negative error code otherwise.
+ */
+static int viortc_class_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct viortc_class *viortc_class;
+	time64_t alarm_time_sec;
+	u64 alarm_time_ns;
+	bool enabled;
+	int ret;
+
+	viortc_class = viortc_class_get_locked(dev);
+	if (IS_ERR(viortc_class))
+		return PTR_ERR(viortc_class);
+
+	ret = viortc_read_alarm(viortc_class->viortc, viortc_class->vio_clk_id,
+				&alarm_time_ns, &enabled);
+	if (ret)
+		return ret;
+
+	alarm_time_sec = div_u64(alarm_time_ns, NSEC_PER_SEC);
+	rtc_time64_to_tm(alarm_time_sec, &alrm->time);
+
+	alrm->enabled = enabled;
+
+	return 0;
+}
+
+/**
+ * viortc_class_set_alarm() - RTC class op set_alarm
+ * @dev: virtio device
+ * @alrm: alarm to set
+ *
+ * Context: Process context.
+ * Return: Zero on success, negative error code otherwise.
+ */
+static int viortc_class_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct viortc_class *viortc_class;
+	time64_t alarm_time_sec;
+	u64 alarm_time_ns;
+
+	viortc_class = viortc_class_get_locked(dev);
+	if (IS_ERR(viortc_class))
+		return PTR_ERR(viortc_class);
+
+	alarm_time_sec = rtc_tm_to_time64(&alrm->time);
+
+	if (alarm_time_sec < 0)
+		return -EINVAL;
+
+	if (check_mul_overflow((u64)alarm_time_sec, (u64)NSEC_PER_SEC,
+			       &alarm_time_ns))
+		return -EINVAL;
+
+	return viortc_set_alarm(viortc_class->viortc, viortc_class->vio_clk_id,
+				alarm_time_ns, alrm->enabled);
+}
+
+/**
+ * viortc_class_alarm_irq_enable() - RTC class op alarm_irq_enable
+ * @dev: virtio device
+ * @enabled: enable or disable alarm IRQ
+ *
+ * Context: Process context.
+ * Return: Zero on success, negative error code otherwise.
+ */
+static int viortc_class_alarm_irq_enable(struct device *dev,
+					 unsigned int enabled)
+{
+	struct viortc_class *viortc_class;
+
+	viortc_class = viortc_class_get_locked(dev);
+	if (IS_ERR(viortc_class))
+		return PTR_ERR(viortc_class);
+
+	return viortc_set_alarm_enabled(viortc_class->viortc,
+					viortc_class->vio_clk_id, enabled);
+}
+
+static const struct rtc_class_ops viortc_class_ops = {
+	.read_time = viortc_class_read_time,
+	.read_alarm = viortc_class_read_alarm,
+	.set_alarm = viortc_class_set_alarm,
+	.alarm_irq_enable = viortc_class_alarm_irq_enable,
+};
+
+/**
+ * viortc_class_alarm() - propagate alarm notification as alarm interrupt
+ * @viortc_class: RTC class wrapper
+ * @vio_clk_id: virtio_rtc clock id
+ *
+ * Context: Any context.
+ */
+void viortc_class_alarm(struct viortc_class *viortc_class, u16 vio_clk_id)
+{
+	if (vio_clk_id != viortc_class->vio_clk_id) {
+		dev_warn_ratelimited(&viortc_class->rtc->dev,
+				     "ignoring alarm for clock id %d, expected id %d\n",
+				     vio_clk_id, viortc_class->vio_clk_id);
+		return;
+	}
+
+	rtc_update_irq(viortc_class->rtc, 1, RTC_AF | RTC_IRQF);
+}
+
+/**
+ * viortc_class_stop() - disallow RTC class ops
+ * @viortc_class: RTC class wrapper
+ *
+ * Context: Process context. Caller must NOT hold rtc_lock().
+ */
+void viortc_class_stop(struct viortc_class *viortc_class)
+{
+	rtc_lock(viortc_class->rtc);
+
+	viortc_class->stopped = true;
+
+	rtc_unlock(viortc_class->rtc);
+}
+
+/**
+ * viortc_class_register() - register RTC class device
+ * @viortc_class: RTC class wrapper
+ *
+ * Context: Process context.
+ * Return: Zero on success, negative error code otherwise.
+ */
+int viortc_class_register(struct viortc_class *viortc_class)
+{
+	return devm_rtc_register_device(viortc_class->rtc);
+}
+
+/**
+ * viortc_class_init() - init RTC class wrapper and device
+ * @viortc: device data
+ * @vio_clk_id: virtio_rtc clock id
+ * @have_alarm: have alarm feature
+ * @parent_dev: virtio device
+ *
+ * Context: Process context.
+ * Return: RTC class wrapper on success, ERR_PTR otherwise.
+ */
+struct viortc_class *viortc_class_init(struct viortc_dev *viortc,
+				       u16 vio_clk_id, bool have_alarm,
+				       struct device *parent_dev)
+{
+	struct viortc_class *viortc_class;
+	struct rtc_device *rtc;
+
+	viortc_class =
+		devm_kzalloc(parent_dev, sizeof(*viortc_class), GFP_KERNEL);
+	if (!viortc_class)
+		return ERR_PTR(-ENOMEM);
+
+	rtc = devm_rtc_allocate_device(parent_dev);
+	if (IS_ERR(rtc))
+		return ERR_CAST(rtc);
+
+	viortc_class->viortc = viortc;
+	viortc_class->rtc = rtc;
+	viortc_class->vio_clk_id = vio_clk_id;
+
+	if (!have_alarm)
+		clear_bit(RTC_FEATURE_ALARM, rtc->features);
+	clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features);
+
+	rtc->ops = &viortc_class_ops;
+	rtc->range_max = div_u64(U64_MAX, NSEC_PER_SEC);
+
+	return viortc_class;
+}
--- a/drivers/virtio/virtio_rtc_driver.c
+++ b/drivers/virtio/virtio_rtc_driver.c
--- a/drivers/virtio/virtio_rtc_internal.h
+++ b/drivers/virtio/virtio_rtc_internal.h
@@ -0,0 +1,122 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * virtio_rtc internal interfaces
+ *
+ * Copyright (C) 2022-2023 OpenSynergy GmbH
+ * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#ifndef _VIRTIO_RTC_INTERNAL_H_
+#define _VIRTIO_RTC_INTERNAL_H_
+
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/ptp_clock_kernel.h>
+#include <linux/types.h>
+
+/* driver core IFs */
+
+struct viortc_dev;
+
+int viortc_read(struct viortc_dev *viortc, u16 vio_clk_id, u64 *reading);
+int viortc_read_cross(struct viortc_dev *viortc, u16 vio_clk_id, u8 hw_counter,
+		      u64 *reading, u64 *cycles);
+int viortc_cross_cap(struct viortc_dev *viortc, u16 vio_clk_id, u8 hw_counter,
+		     bool *supported);
+int viortc_read_alarm(struct viortc_dev *viortc, u16 vio_clk_id,
+		      u64 *alarm_time, bool *enabled);
+int viortc_set_alarm(struct viortc_dev *viortc, u16 vio_clk_id, u64 alarm_time,
+		     bool alarm_enable);
+int viortc_set_alarm_enabled(struct viortc_dev *viortc, u16 vio_clk_id,
+			     bool alarm_enable);
+
+struct viortc_class;
+
+struct viortc_class *viortc_class_from_dev(struct device *dev);
+
+/* PTP IFs */
+
+struct viortc_ptp_clock;
+
+#if IS_ENABLED(CONFIG_VIRTIO_RTC_PTP)
+
+struct viortc_ptp_clock *viortc_ptp_register(struct viortc_dev *viortc,
+					     struct device *parent_dev,
+					     u16 vio_clk_id,
+					     const char *ptp_clock_name);
+int viortc_ptp_unregister(struct viortc_ptp_clock *vio_ptp,
+			  struct device *parent_dev);
+
+#else
+
+static inline struct viortc_ptp_clock *
+viortc_ptp_register(struct viortc_dev *viortc, struct device *parent_dev,
+		    u16 vio_clk_id, const char *ptp_clock_name)
+{
+	return NULL;
+}
+
+static inline int viortc_ptp_unregister(struct viortc_ptp_clock *vio_ptp,
+					struct device *parent_dev)
+{
+	return -ENODEV;
+}
+
+#endif
+
+/* HW counter IFs */
+
+/**
+ * viortc_hw_xtstamp_params() - get HW-specific xtstamp params
+ * @hw_counter: virtio_rtc HW counter type
+ * @cs_id: clocksource id corresponding to hw_counter
+ *
+ * Gets the HW-specific xtstamp params. Returns an error if the driver cannot
+ * support xtstamp.
+ *
+ * Context: Process context.
+ * Return: Zero on success, negative error code otherwise.
+ */
+int viortc_hw_xtstamp_params(u8 *hw_counter, enum clocksource_ids *cs_id);
+
+/* RTC class IFs */
+
+#if IS_ENABLED(CONFIG_VIRTIO_RTC_CLASS)
+
+void viortc_class_alarm(struct viortc_class *viortc_class, u16 vio_clk_id);
+
+void viortc_class_stop(struct viortc_class *viortc_class);
+
+int viortc_class_register(struct viortc_class *viortc_class);
+
+struct viortc_class *viortc_class_init(struct viortc_dev *viortc,
+				       u16 vio_clk_id, bool have_alarm,
+				       struct device *parent_dev);
+
+#else /* CONFIG_VIRTIO_RTC_CLASS */
+
+static inline void viortc_class_alarm(struct viortc_class *viortc_class,
+				      u16 vio_clk_id)
+{
+}
+
+static inline void viortc_class_stop(struct viortc_class *viortc_class)
+{
+}
+
+static inline int viortc_class_register(struct viortc_class *viortc_class)
+{
+	return -ENODEV;
+}
+
+static inline struct viortc_class *viortc_class_init(struct viortc_dev *viortc,
+						     u16 vio_clk_id,
+						     bool have_alarm,
+						     struct device *parent_dev)
+{
+	return ERR_PTR(-ENODEV);
+}
+
+#endif /* CONFIG_VIRTIO_RTC_CLASS */
+
+#endif /* _VIRTIO_RTC_INTERNAL_H_ */
--- a/drivers/virtio/virtio_rtc_ptp.c
+++ b/drivers/virtio/virtio_rtc_ptp.c
@@ -0,0 +1,347 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Expose virtio_rtc clocks as PTP clocks.
+ *
+ * Copyright (C) 2022-2023 OpenSynergy GmbH
+ * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ *
+ * Derived from ptp_kvm_common.c, virtual PTP 1588 clock for use with KVM
+ * guests.
+ *
+ * Copyright (C) 2017 Red Hat Inc.
+ */
+
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/ptp_clock_kernel.h>
+
+#include <uapi/linux/virtio_rtc.h>
+
+#include "virtio_rtc_internal.h"
+
+/**
+ * struct viortc_ptp_clock - PTP clock abstraction
+ * @ptp_clock: PTP clock handle for unregistering
+ * @viortc: virtio_rtc device data
+ * @ptp_info: PTP clock description
+ * @vio_clk_id: virtio_rtc clock id
+ * @have_cross: device supports crosststamp with available HW counter
+ */
+struct viortc_ptp_clock {
+	struct ptp_clock *ptp_clock;
+	struct viortc_dev *viortc;
+	struct ptp_clock_info ptp_info;
+	u16 vio_clk_id;
+	bool have_cross;
+};
+
+/**
+ * struct viortc_ptp_cross_ctx - context for get_device_system_crosststamp()
+ * @device_time: device clock reading
+ * @system_counterval: HW counter value at device_time
+ *
+ * Provides the already obtained crosststamp to get_device_system_crosststamp().
+ */
+struct viortc_ptp_cross_ctx {
+	ktime_t device_time;
+	struct system_counterval_t system_counterval;
+};
+
+/* Weak function in case get_device_system_crosststamp() is not supported */
+int __weak viortc_hw_xtstamp_params(u8 *hw_counter, enum clocksource_ids *cs_id)
+{
+	return -EOPNOTSUPP;
+}
+
+/**
+ * viortc_ptp_get_time_fn() - callback for get_device_system_crosststamp()
+ * @device_time: device clock reading
+ * @system_counterval: HW counter value at device_time
+ * @ctx: context with already obtained crosststamp
+ *
+ * Return: zero (success).
+ */
+static int viortc_ptp_get_time_fn(ktime_t *device_time,
+				  struct system_counterval_t *system_counterval,
+				  void *ctx)
+{
+	struct viortc_ptp_cross_ctx *vio_ctx = ctx;
+
+	*device_time = vio_ctx->device_time;
+	*system_counterval = vio_ctx->system_counterval;
+
+	return 0;
+}
+
+/**
+ * viortc_ptp_do_xtstamp() - get crosststamp from device
+ * @vio_ptp: virtio_rtc PTP clock
+ * @hw_counter: virtio_rtc HW counter type
+ * @cs_id: clocksource id corresponding to hw_counter
+ * @ctx: context for get_device_system_crosststamp()
+ *
+ * Reads HW-specific crosststamp from device.
+ *
+ * Context: Process context.
+ * Return: Zero on success, negative error code otherwise.
+ */
+static int viortc_ptp_do_xtstamp(struct viortc_ptp_clock *vio_ptp,
+				 u8 hw_counter, enum clocksource_ids cs_id,
+				 struct viortc_ptp_cross_ctx *ctx)
+{
+	u64 max_ns, ns;
+	int ret;
+
+	ctx->system_counterval.cs_id = cs_id;
+
+	ret = viortc_read_cross(vio_ptp->viortc, vio_ptp->vio_clk_id,
+				hw_counter, &ns,
+				&ctx->system_counterval.cycles);
+	if (ret)
+		return ret;
+
+	max_ns = (u64)ktime_to_ns(KTIME_MAX);
+	if (ns > max_ns)
+		return -EINVAL;
+
+	ctx->device_time = ns_to_ktime(ns);
+
+	return 0;
+}
+
+/*
+ * PTP clock operations
+ */
+
+/**
+ * viortc_ptp_getcrosststamp() - PTP clock getcrosststamp op
+ * @ptp: PTP clock info
+ * @xtstamp: crosststamp
+ *
+ * Context: Process context.
+ * Return: Zero on success, negative error code otherwise.
+ */
+static int viortc_ptp_getcrosststamp(struct ptp_clock_info *ptp,
+				     struct system_device_crosststamp *xtstamp)
+{
+	struct viortc_ptp_clock *vio_ptp =
+		container_of(ptp, struct viortc_ptp_clock, ptp_info);
+	struct system_time_snapshot history_begin;
+	struct viortc_ptp_cross_ctx ctx;
+	enum clocksource_ids cs_id;
+	u8 hw_counter;
+	int ret;
+
+	if (!vio_ptp->have_cross)
+		return -EOPNOTSUPP;
+
+	ret = viortc_hw_xtstamp_params(&hw_counter, &cs_id);
+	if (ret)
+		return ret;
+
+	ktime_get_snapshot(&history_begin);
+	if (history_begin.cs_id != cs_id)
+		return -EOPNOTSUPP;
+
+	/*
+	 * Getting the timestamp can take many milliseconds with a slow Virtio
+	 * device. This is too long for viortc_ptp_get_time_fn() passed to
+	 * get_device_system_crosststamp(), which has to usually return before
+	 * the timekeeper seqcount increases (every tick or so).
+	 *
+	 * So, get the actual cross-timestamp first.
+	 */
+	ret = viortc_ptp_do_xtstamp(vio_ptp, hw_counter, cs_id, &ctx);
+	if (ret)
+		return ret;
+
+	ret = get_device_system_crosststamp(viortc_ptp_get_time_fn, &ctx,
+					    &history_begin, xtstamp);
+	if (ret)
+		pr_debug("%s: get_device_system_crosststamp() returned %d\n",
+			 __func__, ret);
+
+	return ret;
+}
+
+/* viortc_ptp_adjfine() - unsupported PTP clock adjfine op */
+static int viortc_ptp_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
+{
+	return -EOPNOTSUPP;
+}
+
+/* viortc_ptp_adjtime() - unsupported PTP clock adjtime op */
+static int viortc_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
+{
+	return -EOPNOTSUPP;
+}
+
+/* viortc_ptp_settime64() - unsupported PTP clock settime64 op */
+static int viortc_ptp_settime64(struct ptp_clock_info *ptp,
+				const struct timespec64 *ts)
+{
+	return -EOPNOTSUPP;
+}
+
+/*
+ * viortc_ptp_gettimex64() - PTP clock gettimex64 op
+ *
+ * Context: Process context.
+ */
+static int viortc_ptp_gettimex64(struct ptp_clock_info *ptp,
+				 struct timespec64 *ts,
+				 struct ptp_system_timestamp *sts)
+{
+	struct viortc_ptp_clock *vio_ptp =
+		container_of(ptp, struct viortc_ptp_clock, ptp_info);
+	int ret;
+	u64 ns;
+
+	ptp_read_system_prets(sts);
+	ret = viortc_read(vio_ptp->viortc, vio_ptp->vio_clk_id, &ns);
+	ptp_read_system_postts(sts);
+
+	if (ret)
+		return ret;
+
+	if (ns > (u64)S64_MAX)
+		return -EINVAL;
+
+	*ts = ns_to_timespec64((s64)ns);
+
+	return 0;
+}
+
+/* viortc_ptp_enable() - unsupported PTP clock enable op */
+static int viortc_ptp_enable(struct ptp_clock_info *ptp,
+			     struct ptp_clock_request *rq, int on)
+{
+	return -EOPNOTSUPP;
+}
+
+/*
+ * viortc_ptp_info_template - ptp_clock_info template
+ *
+ * The .name member will be set for individual virtio_rtc PTP clocks.
+ *
+ * The .getcrosststamp member will be cleared for PTP clocks not supporting
+ * crosststamp.
+ */
+static const struct ptp_clock_info viortc_ptp_info_template = {
+	.owner = THIS_MODULE,
+	/* .name is set according to clock type */
+	.adjfine = viortc_ptp_adjfine,
+	.adjtime = viortc_ptp_adjtime,
+	.gettimex64 = viortc_ptp_gettimex64,
+	.settime64 = viortc_ptp_settime64,
+	.enable = viortc_ptp_enable,
+	.getcrosststamp = viortc_ptp_getcrosststamp,
+};
+
+/**
+ * viortc_ptp_unregister() - PTP clock unregistering wrapper
+ * @vio_ptp: virtio_rtc PTP clock
+ * @parent_dev: parent device of PTP clock
+ *
+ * Return: Zero on success, negative error code otherwise.
+ */
+int viortc_ptp_unregister(struct viortc_ptp_clock *vio_ptp,
+			  struct device *parent_dev)
+{
+	int ret = ptp_clock_unregister(vio_ptp->ptp_clock);
+
+	if (!ret)
+		devm_kfree(parent_dev, vio_ptp);
+
+	return ret;
+}
+
+/**
+ * viortc_ptp_get_cross_cap() - get xtstamp support info from device
+ * @viortc: virtio_rtc device data
+ * @vio_ptp: virtio_rtc PTP clock abstraction
+ *
+ * Context: Process context.
+ * Return: Zero on success, negative error code otherwise.
+ */
+static int viortc_ptp_get_cross_cap(struct viortc_dev *viortc,
+				    struct viortc_ptp_clock *vio_ptp)
+{
+	enum clocksource_ids cs_id;
+	bool xtstamp_supported;
+	u8 hw_counter;
+	int ret;
+
+	ret = viortc_hw_xtstamp_params(&hw_counter, &cs_id);
+	if (ret) {
+		vio_ptp->have_cross = false;
+		return 0;
+	}
+
+	ret = viortc_cross_cap(viortc, vio_ptp->vio_clk_id, hw_counter,
+			       &xtstamp_supported);
+	if (ret)
+		return ret;
+
+	vio_ptp->have_cross = xtstamp_supported;
+
+	return 0;
+}
+
+/**
+ * viortc_ptp_register() - prepare and register PTP clock
+ * @viortc: virtio_rtc device data
+ * @parent_dev: parent device for PTP clock
+ * @vio_clk_id: id of virtio_rtc clock which backs PTP clock
+ * @ptp_clock_name: PTP clock name
+ *
+ * Context: Process context.
+ * Return: Pointer on success, ERR_PTR() otherwise; NULL if PTP clock support
+ *         not available.
+ */
+struct viortc_ptp_clock *viortc_ptp_register(struct viortc_dev *viortc,
+					     struct device *parent_dev,
+					     u16 vio_clk_id,
+					     const char *ptp_clock_name)
+{
+	struct viortc_ptp_clock *vio_ptp;
+	struct ptp_clock *ptp_clock;
+	ssize_t len;
+	int ret;
+
+	vio_ptp = devm_kzalloc(parent_dev, sizeof(*vio_ptp), GFP_KERNEL);
+	if (!vio_ptp)
+		return ERR_PTR(-ENOMEM);
+
+	vio_ptp->viortc = viortc;
+	vio_ptp->vio_clk_id = vio_clk_id;
+	vio_ptp->ptp_info = viortc_ptp_info_template;
+	len = strscpy(vio_ptp->ptp_info.name, ptp_clock_name,
+		      sizeof(vio_ptp->ptp_info.name));
+	if (len < 0) {
+		ret = len;
+		goto err_free_dev;
+	}
+
+	ret = viortc_ptp_get_cross_cap(viortc, vio_ptp);
+	if (ret)
+		goto err_free_dev;
+
+	if (!vio_ptp->have_cross)
+		vio_ptp->ptp_info.getcrosststamp = NULL;
+
+	ptp_clock = ptp_clock_register(&vio_ptp->ptp_info, parent_dev);
+	if (IS_ERR(ptp_clock))
+		goto err_on_register;
+
+	vio_ptp->ptp_clock = ptp_clock;
+
+	return vio_ptp;
+
+err_on_register:
+	ret = PTR_ERR(ptp_clock);
+
+err_free_dev:
+	devm_kfree(parent_dev, vio_ptp);
+	return ERR_PTR(ret);
+}
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -329,6 +329,8 @@ static inline
 bool virtio_get_shm_region(struct virtio_device *vdev,
 			   struct virtio_shm_region *region, u8 id)
 {
+	if (!region->len)
+		return false;
 	if (!vdev->config->get_shm_region)
 		return false;
 	return vdev->config->get_shm_region(vdev, region, id);
--- a/include/uapi/linux/virtio_rtc.h
+++ b/include/uapi/linux/virtio_rtc.h
@@ -0,0 +1,237 @@
+/* SPDX-License-Identifier: ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) */
+/*
+ * Copyright (C) 2022-2024 OpenSynergy GmbH
+ * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#ifndef _LINUX_VIRTIO_RTC_H
+#define _LINUX_VIRTIO_RTC_H
+
+#include <linux/types.h>
+
+/* alarm feature */
+#define VIRTIO_RTC_F_ALARM	0
+
+/* read request message types */
+
+#define VIRTIO_RTC_REQ_READ			0x0001
+#define VIRTIO_RTC_REQ_READ_CROSS		0x0002
+
+/* control request message types */
+
+#define VIRTIO_RTC_REQ_CFG			0x1000
+#define VIRTIO_RTC_REQ_CLOCK_CAP		0x1001
+#define VIRTIO_RTC_REQ_CROSS_CAP		0x1002
+#define VIRTIO_RTC_REQ_READ_ALARM		0x1003
+#define VIRTIO_RTC_REQ_SET_ALARM		0x1004
+#define VIRTIO_RTC_REQ_SET_ALARM_ENABLED	0x1005
+
+/* alarmq message types */
+
+#define VIRTIO_RTC_NOTIF_ALARM			0x2000
+
+/* Message headers */
+
+/** common request header */
+struct virtio_rtc_req_head {
+	__le16 msg_type;
+	__u8 reserved[6];
+};
+
+/** common response header */
+struct virtio_rtc_resp_head {
+#define VIRTIO_RTC_S_OK			0
+#define VIRTIO_RTC_S_EOPNOTSUPP		2
+#define VIRTIO_RTC_S_ENODEV		3
+#define VIRTIO_RTC_S_EINVAL		4
+#define VIRTIO_RTC_S_EIO		5
+	__u8 status;
+	__u8 reserved[7];
+};
+
+/** common notification header */
+struct virtio_rtc_notif_head {
+	__le16 msg_type;
+	__u8 reserved[6];
+};
+
+/* read requests */
+
+/* VIRTIO_RTC_REQ_READ message */
+
+struct virtio_rtc_req_read {
+	struct virtio_rtc_req_head head;
+	__le16 clock_id;
+	__u8 reserved[6];
+};
+
+struct virtio_rtc_resp_read {
+	struct virtio_rtc_resp_head head;
+	__le64 clock_reading;
+};
+
+/* VIRTIO_RTC_REQ_READ_CROSS message */
+
+struct virtio_rtc_req_read_cross {
+	struct virtio_rtc_req_head head;
+	__le16 clock_id;
+/* Arm Generic Timer Counter-timer Virtual Count Register (CNTVCT_EL0) */
+#define VIRTIO_RTC_COUNTER_ARM_VCT	0
+/* x86 Time-Stamp Counter */
+#define VIRTIO_RTC_COUNTER_X86_TSC	1
+/* Invalid */
+#define VIRTIO_RTC_COUNTER_INVALID	0xFF
+	__u8 hw_counter;
+	__u8 reserved[5];
+};
+
+struct virtio_rtc_resp_read_cross {
+	struct virtio_rtc_resp_head head;
+	__le64 clock_reading;
+	__le64 counter_cycles;
+};
+
+/* control requests */
+
+/* VIRTIO_RTC_REQ_CFG message */
+
+struct virtio_rtc_req_cfg {
+	struct virtio_rtc_req_head head;
+	/* no request params */
+};
+
+struct virtio_rtc_resp_cfg {
+	struct virtio_rtc_resp_head head;
+	/** # of clocks -> clock ids < num_clocks are valid */
+	__le16 num_clocks;
+	__u8 reserved[6];
+};
+
+/* VIRTIO_RTC_REQ_CLOCK_CAP message */
+
+struct virtio_rtc_req_clock_cap {
+	struct virtio_rtc_req_head head;
+	__le16 clock_id;
+	__u8 reserved[6];
+};
+
+struct virtio_rtc_resp_clock_cap {
+	struct virtio_rtc_resp_head head;
+#define VIRTIO_RTC_CLOCK_UTC			0
+#define VIRTIO_RTC_CLOCK_TAI			1
+#define VIRTIO_RTC_CLOCK_MONOTONIC		2
+#define VIRTIO_RTC_CLOCK_UTC_SMEARED		3
+#define VIRTIO_RTC_CLOCK_UTC_MAYBE_SMEARED	4
+	__u8 type;
+#define VIRTIO_RTC_SMEAR_UNSPECIFIED	0
+#define VIRTIO_RTC_SMEAR_NOON_LINEAR	1
+#define VIRTIO_RTC_SMEAR_UTC_SLS	2
+	__u8 leap_second_smearing;
+#define VIRTIO_RTC_FLAG_ALARM_CAP		(1 << 0)
+	__u8 flags;
+	__u8 reserved[5];
+};
+
+/* VIRTIO_RTC_REQ_CROSS_CAP message */
+
+struct virtio_rtc_req_cross_cap {
+	struct virtio_rtc_req_head head;
+	__le16 clock_id;
+	__u8 hw_counter;
+	__u8 reserved[5];
+};
+
+struct virtio_rtc_resp_cross_cap {
+	struct virtio_rtc_resp_head head;
+#define VIRTIO_RTC_FLAG_CROSS_CAP	(1 << 0)
+	__u8 flags;
+	__u8 reserved[7];
+};
+
+/* VIRTIO_RTC_REQ_READ_ALARM message */
+
+struct virtio_rtc_req_read_alarm {
+	struct virtio_rtc_req_head head;
+	__le16 clock_id;
+	__u8 reserved[6];
+};
+
+struct virtio_rtc_resp_read_alarm {
+	struct virtio_rtc_resp_head head;
+	__le64 alarm_time;
+#define VIRTIO_RTC_FLAG_ALARM_ENABLED	(1 << 0)
+	__u8 flags;
+	__u8 reserved[7];
+};
+
+/* VIRTIO_RTC_REQ_SET_ALARM message */
+
+struct virtio_rtc_req_set_alarm {
+	struct virtio_rtc_req_head head;
+	__le64 alarm_time;
+	__le16 clock_id;
+	/* flag VIRTIO_RTC_FLAG_ALARM_ENABLED */
+	__u8 flags;
+	__u8 reserved[5];
+};
+
+struct virtio_rtc_resp_set_alarm {
+	struct virtio_rtc_resp_head head;
+	/* no response params */
+};
+
+/* VIRTIO_RTC_REQ_SET_ALARM_ENABLED message */
+
+struct virtio_rtc_req_set_alarm_enabled {
+	struct virtio_rtc_req_head head;
+	__le16 clock_id;
+	/* flag VIRTIO_RTC_ALARM_ENABLED */
+	__u8 flags;
+	__u8 reserved[5];
+};
+
+struct virtio_rtc_resp_set_alarm_enabled {
+	struct virtio_rtc_resp_head head;
+	/* no response params */
+};
+
+/** Union of request types for requestq */
+union virtio_rtc_req_requestq {
+	struct virtio_rtc_req_read read;
+	struct virtio_rtc_req_read_cross read_cross;
+	struct virtio_rtc_req_cfg cfg;
+	struct virtio_rtc_req_clock_cap clock_cap;
+	struct virtio_rtc_req_cross_cap cross_cap;
+	struct virtio_rtc_req_read_alarm read_alarm;
+	struct virtio_rtc_req_set_alarm set_alarm;
+	struct virtio_rtc_req_set_alarm_enabled set_alarm_enabled;
+};
+
+/** Union of response types for requestq */
+union virtio_rtc_resp_requestq {
+	struct virtio_rtc_resp_read read;
+	struct virtio_rtc_resp_read_cross read_cross;
+	struct virtio_rtc_resp_cfg cfg;
+	struct virtio_rtc_resp_clock_cap clock_cap;
+	struct virtio_rtc_resp_cross_cap cross_cap;
+	struct virtio_rtc_resp_read_alarm read_alarm;
+	struct virtio_rtc_resp_set_alarm set_alarm;
+	struct virtio_rtc_resp_set_alarm_enabled set_alarm_enabled;
+};
+
+/* alarmq notifications */
+
+/* VIRTIO_RTC_NOTIF_ALARM notification */
+
+struct virtio_rtc_notif_alarm {
+	struct virtio_rtc_notif_head head;
+	__le16 clock_id;
+	__u8 reserved[6];
+};
+
+/** Union of notification types for alarmq */
+union virtio_rtc_notif_alarmq {
+	struct virtio_rtc_notif_alarm alarm;
+};
+
+#endif /* _LINUX_VIRTIO_RTC_H */