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McKenney" , Boqun Feng , Arjun Roy , linux-kernel , Eric Dumazet , Eric Dumazet Subject: [PATCH v3 1/3] rseq: optimize rseq_update_cpu_id() Date: Tue, 13 Apr 2021 13:33:50 -0700 Message-Id: <20210413203352.71350-2-eric.dumazet@gmail.com> X-Mailer: git-send-email 2.31.1.295.g9ea45b61b8-goog In-Reply-To: <20210413203352.71350-1-eric.dumazet@gmail.com> References: <20210413203352.71350-1-eric.dumazet@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eric Dumazet 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 Cc: Mathieu Desnoyers Cc: Peter Zijlstra Cc: "Paul E. McKenney" Cc: Boqun Feng Cc: Arjun Roy Cc: Ingo Molnar --- kernel/rseq.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/kernel/rseq.c b/kernel/rseq.c index a4f86a9d6937cdfa2f13d1dcc9be863c1943d06f..f020f18f512a3f6241c3c9b104ce50e4d2c6188c 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) -- 2.31.1.295.g9ea45b61b8-goog