----- On Apr 13, 2021, at 3:36 AM, Eric Dumazet eric.duma...@gmail.com wrote:
> From: Eric Dumazet <eduma...@google.com>
>
> 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 <eduma...@google.com>
> Cc: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: "Paul E. McKenney" <paul...@kernel.org>
> Cc: Boqun Feng <boqun.f...@gmail.com>
> Cc: Arjun Roy <arjun...@google.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> ---
> kernel/rseq.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/rseq.c b/kernel/rseq.c
> index
> a4f86a9d6937cdfa2f13d1dcc9be863c1943d06f..d2689ccbb132c0fc8ec0924008771e5ee1ca855e
> 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 *r = t->rseq;
AFAIU the variable above should be a struct rseq __user *.
Elsewhere in the file we use "rseq" rather than "r" for struct rseq __user *
variable name, it would be better to keep the naming consistent across the file
if possible.
Thanks,
Mathieu
>
> - 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(r, sizeof(*r)))
> + goto efault;
> + unsafe_put_user(cpu_id, &r->cpu_id_start, efault_end);
> + unsafe_put_user(cpu_id, &r->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)
> --
> 2.31.1.295.g9ea45b61b8-goog
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
