[tip: sched/core] rseq: Optimise rseq_get_rseq_cs() and clear_rseq_cs()

[tip-bot2 for Eric Dumazet]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     5e0ccd4a3b01c5a71732a13186ca110a138516ea
Gitweb:        https://git.kernel.org/tip/5e0ccd4a3b01c5a71732a13186ca110a138516ea
Author:        Eric Dumazet <edumazet@xxxxxxxxxx>
AuthorDate:    Tue, 13 Apr 2021 13:33:52 -07:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 14 Apr 2021 18:04:09 +02:00

rseq: Optimise rseq_get_rseq_cs() and clear_rseq_cs()

Commit ec9c82e03a74 ("rseq: uapi: Declare rseq_cs field as union,
update includes") added regressions for our servers.

Using copy_from_user() and clear_user() for 64bit values
is suboptimal.

We can use faster put_user() and get_user() on 64bit arches.

Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210413203352.71350-4-eric.dumazet@xxxxxxxxx
---
 kernel/rseq.c |  9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/rseq.c b/kernel/rseq.c
index cfe01ab..35f7bd0 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -127,8 +127,13 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
 	u32 sig;
 	int ret;
 
+#ifdef CONFIG_64BIT
+	if (get_user(ptr, &t->rseq->rseq_cs.ptr64))
+		return -EFAULT;
+#else
 	if (copy_from_user(&ptr, &t->rseq->rseq_cs.ptr64, sizeof(ptr)))
 		return -EFAULT;
+#endif
 	if (!ptr) {
 		memset(rseq_cs, 0, sizeof(*rseq_cs));
 		return 0;
@@ -211,9 +216,13 @@ static int clear_rseq_cs(struct task_struct *t)
 	 *
 	 * Set rseq_cs to NULL.
 	 */
+#ifdef CONFIG_64BIT
+	return put_user(0UL, &t->rseq->rseq_cs.ptr64);
+#else
 	if (clear_user(&t->rseq->rseq_cs.ptr64, sizeof(t->rseq->rseq_cs.ptr64)))
 		return -EFAULT;
 	return 0;
+#endif
 }
 
 /*