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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
This commit is contained in:
Eric Dumazet 2021-04-13 13:33:50 -07:00 committed by Peter Zijlstra
parent 4bad58ebc8
commit 60af388d23
1 changed files with 11 additions and 4 deletions
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15
kernel/rseq.c
View File

@ -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)