[PATCH v3 0/3] rseq: minor optimizations

[PATCH v3 0/3] rseq: minor optimizations

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

rseq is a heavy user of copy to/from user data in fast paths.
This series tries to reduce the cost.

v3: Third patch going back to v1 (only deal with 64bit arches)
v2: Addressed Peter and Mathieu feedbacks, thanks !

Eric Dumazet (3):
  rseq: optimize rseq_update_cpu_id()
  rseq: remove redundant access_ok()
  rseq: optimise rseq_get_rseq_cs() and clear_rseq_cs()

 kernel/rseq.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

-- 
2.31.1.295.g9ea45b61b8-goog

[PATCH v3 1/3] rseq: optimize rseq_update_cpu_id()

[Eric Dumazet]

From: Eric Dumazet <edumazet@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 <edumazet@google.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Ingo Molnar <mingo@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..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

[PATCH v3 2/3] rseq: remove redundant access_ok()

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

After commit 8f2817701492 ("rseq: Use get_user/put_user rather
than __get_user/__put_user") we no longer need
an access_ok() call from __rseq_handle_notify_resume()

Mathieu pointed out the same cleanup can be done
in rseq_syscall().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
---
 kernel/rseq.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/rseq.c b/kernel/rseq.c
index f020f18f512a3f6241c3c9b104ce50e4d2c6188c..cfe01ab5253c1c424c0e8b25acbb6a8e1b41a5b6 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -273,8 +273,6 @@ void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs)
 
 	if (unlikely(t->flags & PF_EXITING))
 		return;
-	if (unlikely(!access_ok(t->rseq, sizeof(*t->rseq))))
-		goto error;
 	ret = rseq_ip_fixup(regs);
 	if (unlikely(ret < 0))
 		goto error;
@@ -301,8 +299,7 @@ void rseq_syscall(struct pt_regs *regs)
 
 	if (!t->rseq)
 		return;
-	if (!access_ok(t->rseq, sizeof(*t->rseq)) ||
-	    rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs))
+	if (rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs))
 		force_sig(SIGSEGV);
 }
 
-- 
2.31.1.295.g9ea45b61b8-goog

[PATCH v3 3/3] rseq: optimise rseq_get_rseq_cs() and clear_rseq_cs()

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

Commit ec9c82e03a74 ("rseq: uapi: Declare rseq_cs field as union,
update includes") added regressions for our servers.

Using copy_from_user() and clear_user() for 64bit values
is suboptimal.

We can use faster put_user() and get_user() on 64bit arches.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
---
 kernel/rseq.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/rseq.c b/kernel/rseq.c
index cfe01ab5253c1c424c0e8b25acbb6a8e1b41a5b6..35f7bd0fced0e2dd8aed819e054dac03f024388a 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -127,8 +127,13 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
 	u32 sig;
 	int ret;
 
+#ifdef CONFIG_64BIT
+	if (get_user(ptr, &t->rseq->rseq_cs.ptr64))
+		return -EFAULT;
+#else
 	if (copy_from_user(&ptr, &t->rseq->rseq_cs.ptr64, sizeof(ptr)))
 		return -EFAULT;
+#endif
 	if (!ptr) {
 		memset(rseq_cs, 0, sizeof(*rseq_cs));
 		return 0;
@@ -211,9 +216,13 @@ static int clear_rseq_cs(struct task_struct *t)
 	 *
 	 * Set rseq_cs to NULL.
 	 */
+#ifdef CONFIG_64BIT
+	return put_user(0UL, &t->rseq->rseq_cs.ptr64);
+#else
 	if (clear_user(&t->rseq->rseq_cs.ptr64, sizeof(t->rseq->rseq_cs.ptr64)))
 		return -EFAULT;
 	return 0;
+#endif
 }
 
 /*
-- 
2.31.1.295.g9ea45b61b8-goog

Re: [PATCH v3 0/3] rseq: minor optimizations

[Mathieu Desnoyers]

----- On Apr 13, 2021, at 4:33 PM, Eric Dumazet eric.dumazet@gmail.com wrote:

> From: Eric Dumazet <edumazet@google.com>
> 
> rseq is a heavy user of copy to/from user data in fast paths.
> This series tries to reduce the cost.
> 
> v3: Third patch going back to v1 (only deal with 64bit arches)
> v2: Addressed Peter and Mathieu feedbacks, thanks !

For the whole series:

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Thanks Eric!

Mathieu

> 
> Eric Dumazet (3):
>  rseq: optimize rseq_update_cpu_id()
>  rseq: remove redundant access_ok()
>  rseq: optimise rseq_get_rseq_cs() and clear_rseq_cs()
> 
> kernel/rseq.c | 29 +++++++++++++++++++++--------
> 1 file changed, 21 insertions(+), 8 deletions(-)
> 
> --
> 2.31.1.295.g9ea45b61b8-goog

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

Re: [PATCH v3 0/3] rseq: minor optimizations

[Peter Zijlstra]

On Tue, Apr 13, 2021 at 04:40:33PM -0400, Mathieu Desnoyers wrote:
> ----- On Apr 13, 2021, at 4:33 PM, Eric Dumazet eric.dumazet@gmail.com wrote:
> 
> > From: Eric Dumazet <edumazet@google.com>
> > 
> > rseq is a heavy user of copy to/from user data in fast paths.
> > This series tries to reduce the cost.
> > 
> > v3: Third patch going back to v1 (only deal with 64bit arches)
> > v2: Addressed Peter and Mathieu feedbacks, thanks !
> 
> For the whole series:
> 
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Thanks!

[tip: sched/core] rseq: Remove redundant access_ok()

[tip-bot2 for Eric Dumazet]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     0ed96051531ecc6965f6456d25b19b9b6bdb5c28
Gitweb:        https://git.kernel.org/tip/0ed96051531ecc6965f6456d25b19b9b6bdb5c28
Author:        Eric Dumazet <edumazet@google.com>
AuthorDate:    Tue, 13 Apr 2021 13:33:51 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 14 Apr 2021 18:04:09 +02:00

rseq: Remove redundant access_ok()

After commit 8f2817701492 ("rseq: Use get_user/put_user rather
than __get_user/__put_user") we no longer need
an access_ok() call from __rseq_handle_notify_resume()

Mathieu pointed out the same cleanup can be done
in rseq_syscall().

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/20210413203352.71350-3-eric.dumazet@gmail.com
---
 kernel/rseq.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/rseq.c b/kernel/rseq.c
index f020f18..cfe01ab 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -273,8 +273,6 @@ void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs)
 
 	if (unlikely(t->flags & PF_EXITING))
 		return;
-	if (unlikely(!access_ok(t->rseq, sizeof(*t->rseq))))
-		goto error;
 	ret = rseq_ip_fixup(regs);
 	if (unlikely(ret < 0))
 		goto error;
@@ -301,8 +299,7 @@ void rseq_syscall(struct pt_regs *regs)
 
 	if (!t->rseq)
 		return;
-	if (!access_ok(t->rseq, sizeof(*t->rseq)) ||
-	    rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs))
+	if (rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs))
 		force_sig(SIGSEGV);
 }
 

[tip: sched/core] rseq: Optimise rseq_get_rseq_cs() and clear_rseq_cs()

[tip-bot2 for Eric Dumazet]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     5e0ccd4a3b01c5a71732a13186ca110a138516ea
Gitweb:        https://git.kernel.org/tip/5e0ccd4a3b01c5a71732a13186ca110a138516ea
Author:        Eric Dumazet <edumazet@google.com>
AuthorDate:    Tue, 13 Apr 2021 13:33:52 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 14 Apr 2021 18:04:09 +02:00

rseq: Optimise rseq_get_rseq_cs() and clear_rseq_cs()

Commit ec9c82e03a74 ("rseq: uapi: Declare rseq_cs field as union,
update includes") added regressions for our servers.

Using copy_from_user() and clear_user() for 64bit values
is suboptimal.

We can use faster put_user() and get_user() on 64bit arches.

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/20210413203352.71350-4-eric.dumazet@gmail.com
---
 kernel/rseq.c |  9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/rseq.c b/kernel/rseq.c
index cfe01ab..35f7bd0 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -127,8 +127,13 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
 	u32 sig;
 	int ret;
 
+#ifdef CONFIG_64BIT
+	if (get_user(ptr, &t->rseq->rseq_cs.ptr64))
+		return -EFAULT;
+#else
 	if (copy_from_user(&ptr, &t->rseq->rseq_cs.ptr64, sizeof(ptr)))
 		return -EFAULT;
+#endif
 	if (!ptr) {
 		memset(rseq_cs, 0, sizeof(*rseq_cs));
 		return 0;
@@ -211,9 +216,13 @@ static int clear_rseq_cs(struct task_struct *t)
 	 *
 	 * Set rseq_cs to NULL.
 	 */
+#ifdef CONFIG_64BIT
+	return put_user(0UL, &t->rseq->rseq_cs.ptr64);
+#else
 	if (clear_user(&t->rseq->rseq_cs.ptr64, sizeof(t->rseq->rseq_cs.ptr64)))
 		return -EFAULT;
 	return 0;
+#endif
 }
 
 /*

[tip: sched/core] rseq: Optimize rseq_update_cpu_id()

[tip-bot2 for Eric Dumazet]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     60af388d23889636011488c42763876bcdda3eab
Gitweb:        https://git.kernel.org/tip/60af388d23889636011488c42763876bcdda3eab
Author:        Eric Dumazet <edumazet@google.com>
AuthorDate:    Tue, 13 Apr 2021 13:33:50 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 14 Apr 2021 18:04:09 +02:00

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
---
 kernel/rseq.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/rseq.c b/kernel/rseq.c
index a4f86a9..f020f18 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)