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authorEric Dumazet <edumazet@google.com>2021-04-13 13:33:50 -0700
committerPeter Zijlstra <peterz@infradead.org>2021-04-14 18:04:09 +0200
commit60af388d23889636011488c42763876bcdda3eab (patch)
tree9fa22b294c260a515a6243a3cc77090b79ec5ec5 /kernel/rseq.c
parent4bad58ebc8bc4f20d89cff95417c9b4674769709 (diff)
downloadlwn-60af388d23889636011488c42763876bcdda3eab.tar.gz
lwn-60af388d23889636011488c42763876bcdda3eab.zip
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
Diffstat (limited to 'kernel/rseq.c')
-rw-r--r--kernel/rseq.c15
1 files changed, 11 insertions, 4 deletions
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)