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virtio_balloon: disable indirect descriptors

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The page reporting callback submits an sg list to the reporting
virtqueue.  With VIRTIO_RING_F_INDIRECT_DESC negotiated and
total_sg > 1 (which it typically is), virtqueue_add reports it to the
host by allocating an indirect descriptor via kmalloc(GFP_KERNEL).

This is not pretty: the reporting worker isolates potentially hundreds
of MB of free pages from the buddy allocator (reported pages are at
least pageblock_order, and the sg can contain up to
PAGE_REPORTING_CAPACITY entries of varying orders).  As the result,
very theoretically, the kmalloc might trigger OOM when we have in fact a
ton of free memory.

Clear VIRTIO_RING_F_INDIRECT_DESC, to avoid using indirect descriptors.

Fixes: b0c504f154 ("virtio-balloon: add support for providing free page reports to host")
Assisted-by: Claude:claude-opus-4-6
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <73fac8a629fd9aca7bb3265ac243a769c28af25d.1783232420.git.mst@redhat.com>
This commit is contained in:
Michael S. Tsirkin
2026-07-05 02:24:18 -04:00
parent fa8833c085
commit 281eb4732a
1 changed files with 6 additions and 0 deletions
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6
drivers/virtio/virtio_balloon.c
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@@ -7,6 +7,7 @@
*/
#include <linux/virtio.h>
#include <uapi/linux/virtio_ring.h>
#include <linux/virtio_balloon.h>
#include <linux/swap.h>
#include <linux/workqueue.h>
@@ -1165,6 +1166,11 @@ static int virtballoon_validate(struct virtio_device *vdev)
else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON))
__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);
/*
* Disable indirect descriptors to avoid memory allocation in
* virtqueue_add during page reporting.
*/
__virtio_clear_bit(vdev, VIRTIO_RING_F_INDIRECT_DESC);
__virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM);
return 0;
}