From 60af388d23889636011488c42763876bcdda3eab Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 13 Apr 2021 13:33:50 -0700 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Mathieu Desnoyers Link: https://lkml.kernel.org/r/20210413203352.71350-2-eric.dumazet@gmail.com --- kernel/rseq.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/kernel/rseq.c b/kernel/rseq.c index a4f86a9..f020f18 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) -- 2.7.4