Commit 60af388d authored by Eric Dumazet's avatar Eric Dumazet Committed by Peter Zijlstra
Browse files

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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lkml.kernel.org/r/20210413203352.71350-2-eric.dumazet@gmail.com
parent 4bad58eb

kernel/rseq.c

+11 −4
Original line number Diff line number Diff line
@@ -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)