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rseq: Cache CPU ID and MM CID values

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In preparation for rewriting RSEQ exit to user space handling provide
storage to cache the CPU ID and MM CID values which were written to user
space. That prepares for a quick check, which avoids the update when
nothing changed.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251027084306.841964081@linutronix.de
This commit is contained in:
Thomas Gleixner
2025-10-27 09:44:45 +01:00
committed by Ingo Molnar
parent 4fc9225d19
commit 4b7de6df20
4 changed files with 32 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/rseq.h
View File

@@ -57,6 +57,7 @@ static inline void rseq_virt_userspace_exit(void)
static inline void rseq_reset(struct task_struct *t)
{
memset(&t->rseq, 0, sizeof(t->rseq));
t->rseq.ids.cpu_cid = ~0ULL;
}
static inline void rseq_execve(struct task_struct *t)
@@ -70,10 +71,12 @@ static inline void rseq_execve(struct task_struct *t)
*/
static inline void rseq_fork(struct task_struct *t, u64 clone_flags)
{
if (clone_flags & CLONE_VM)
if (clone_flags & CLONE_VM) {
rseq_reset(t);
else
} else {
t->rseq = current->rseq;
t->rseq.ids.cpu_cid = ~0ULL;
}
}
#else /* CONFIG_RSEQ */

21
include/linux/rseq_types.h
View File

@@ -30,18 +30,39 @@ struct rseq_event {
};
};
/**
* struct rseq_ids - Cache for ids, which need to be updated
* @cpu_cid: Compound of @cpu_id and @mm_cid to make the
* compiler emit a single compare on 64-bit
* @cpu_id: The CPU ID which was written last to user space
* @mm_cid: The MM CID which was written last to user space
*
* @cpu_id and @mm_cid are updated when the data is written to user space.
*/
struct rseq_ids {
union {
u64 cpu_cid;
struct {
u32 cpu_id;
u32 mm_cid;
};
};
};
/**
* struct rseq_data - Storage for all rseq related data
* @usrptr: Pointer to the registered user space RSEQ memory
* @len: Length of the RSEQ region
* @sig: Signature of critial section abort IPs
* @event: Storage for event management
* @ids: Storage for cached CPU ID and MM CID
*/
struct rseq_data {
struct rseq __user *usrptr;
u32 len;
u32 sig;
struct rseq_event event;
struct rseq_ids ids;
};
#else /* CONFIG_RSEQ */

4
include/trace/events/rseq.h
View File

@@ -21,9 +21,9 @@ TRACE_EVENT(rseq_update,
),
TP_fast_assign(
__entry->cpu_id = raw_smp_processor_id();
__entry->cpu_id = t->rseq.ids.cpu_id;
__entry->node_id = cpu_to_node(__entry->cpu_id);
__entry->mm_cid = task_mm_cid(t);
__entry->mm_cid = t->rseq.ids.mm_cid;
),
TP_printk("cpu_id=%d node_id=%d mm_cid=%d", __entry->cpu_id,

4
kernel/rseq.c
View File

@@ -184,6 +184,10 @@ static int rseq_update_cpu_node_id(struct task_struct *t)
rseq_unsafe_put_user(t, node_id, node_id, efault_end);
rseq_unsafe_put_user(t, mm_cid, mm_cid, efault_end);
/* Cache the user space values */
t->rseq.ids.cpu_id = cpu_id;
t->rseq.ids.mm_cid = mm_cid;
/*
* Additional feature fields added after ORIG_RSEQ_SIZE
* need to be conditionally updated only if