[v3,1/3] rseq: optimize rseq_update_cpu_id()
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Message ID 20210413203352.71350-2-eric.dumazet@gmail.com
State Accepted
Commit 60af388d23889636011488c42763876bcdda3eab
Headers show
  • rseq: minor optimizations
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Commit Message

Eric Dumazet April 13, 2021, 8:33 p.m. UTC
From: Eric Dumazet <edumazet@google.com>

Two put_user() in rseq_update_cpu_id() are replaced
by a pair of unsafe_put_user() with appropriate surroundings.

This removes one stac/clac pair on x86 in fast path.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
 kernel/rseq.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff mbox series

diff --git a/kernel/rseq.c b/kernel/rseq.c
index a4f86a9d6937cdfa2f13d1dcc9be863c1943d06f..f020f18f512a3f6241c3c9b104ce50e4d2c6188c 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -84,13 +84,20 @@ 
 static int rseq_update_cpu_id(struct task_struct *t)
 	u32 cpu_id = raw_smp_processor_id();
+	struct rseq __user *rseq = t->rseq;
-	if (put_user(cpu_id, &t->rseq->cpu_id_start))
-		return -EFAULT;
-	if (put_user(cpu_id, &t->rseq->cpu_id))
-		return -EFAULT;
+	if (!user_write_access_begin(rseq, sizeof(*rseq)))
+		goto efault;
+	unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end);
+	unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end);
+	user_write_access_end();
 	return 0;
+	user_write_access_end();
+	return -EFAULT;
 static int rseq_reset_rseq_cpu_id(struct task_struct *t)