From: Eric Dumazet <edumazet@google.com>
Date: Tue, 13 Apr 2021 20:33:50 +0000 (-0700)
Subject: rseq: Optimize rseq_update_cpu_id()
X-Git-Tag: io_uring-5.13-2021-05-07~33^2~22
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=60af388d23889636011488c42763876bcdda3eab;p=linux-2.6-block.git

rseq: Optimize rseq_update_cpu_id()

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lkml.kernel.org/r/20210413203352.71350-2-eric.dumazet@gmail.com
---

diff --git a/kernel/rseq.c b/kernel/rseq.c
index a4f86a9d6937..f020f18f512a 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();
 	trace_rseq_update(t);
 	return 0;
+
+efault_end:
+	user_write_access_end();
+efault:
+	return -EFAULT;
 }
 
 static int rseq_reset_rseq_cpu_id(struct task_struct *t)