Re: [PATCH] x86: vdso: fix pvclock races with task migration
On 02/04/2015 20:44, Radim Krčmář wrote: If we were migrated right after __getcpu, but before reading the migration_count, we wouldn't notice that we read TSC of a different VCPU, nor that KVM's bug made pvti invalid, as only migration_count on source VCPU is increased. Change vdso instead of updating migration_count on destination. Fixes: 0a4e6be9ca17 (x86: kvm: Revert remove sched notifier for cross-cpu migrations) Cc: sta...@vger.kernel.org Signed-off-by: Radim Krčmář rkrc...@redhat.com Applying this, but removing the Fixes tag because a guest patch cannot fix a host patch (it can work around it or complement it). Paolo -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] x86: vdso: fix pvclock races with task migration
2015-04-07 13:11+0200, Paolo Bonzini: On 02/04/2015 20:44, Radim Krčmář wrote: If we were migrated right after __getcpu, but before reading the migration_count, we wouldn't notice that we read TSC of a different VCPU, nor that KVM's bug made pvti invalid, as only migration_count on source VCPU is increased. Change vdso instead of updating migration_count on destination. Fixes: 0a4e6be9ca17 (x86: kvm: Revert remove sched notifier for cross-cpu migrations) Cc: sta...@vger.kernel.org Signed-off-by: Radim Krčmář rkrc...@redhat.com Applying this, but removing the Fixes tag because a guest patch cannot fix a host patch (it can work around it or complement it). I think it was correct. Both are guest only, the revert just missed some races. (0a4e6be9ca17 has misleading commit message ...) -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] x86: vdso: fix pvclock races with task migration
On 07/04/2015 14:47, Radim Krčmář wrote: I think it was correct. Both are guest only, the revert just missed some races. (0a4e6be9ca17 has misleading commit message ...) Oops. You're right. Paolo -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] x86: vdso: fix pvclock races with task migration
On Thu, Apr 02, 2015 at 08:44:23PM +0200, Radim Krčmář wrote:
If we were migrated right after __getcpu, but before reading the
migration_count, we wouldn't notice that we read TSC of a different
VCPU, nor that KVM's bug made pvti invalid, as only migration_count
on source VCPU is increased.
Change vdso instead of updating migration_count on destination.
Fixes: 0a4e6be9ca17 (x86: kvm: Revert remove sched notifier for cross-cpu
migrations)
Cc: sta...@vger.kernel.org
Signed-off-by: Radim Krčmář rkrc...@redhat.com
---
Because it we'll get a complete rewrite, this series does not
- remove the outdated 'TODO: We can put [...]' comment
- use a proper encapsulation for the inner do-while loop
- optimize the outer do-while loop
(no need to re-read cpu id on version mismatch)
arch/x86/vdso/vclock_gettime.c | 20
1 file changed, 12 insertions(+), 8 deletions(-)
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 30933760ee5f..40d2473836c9 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -99,21 +99,25 @@ static notrace cycle_t vread_pvclock(int *mode)
* __getcpu() calls (Gleb).
*/
- pvti = get_pvti(cpu);
+ /* Make sure migrate_count will change if we leave the VCPU. */
+ do {
+ pvti = get_pvti(cpu);
+ migrate_count = pvti-migrate_count;
- migrate_count = pvti-migrate_count;
+ cpu1 = cpu;
+ cpu = __getcpu() VGETCPU_CPU_MASK;
+ } while (unlikely(cpu != cpu1));
version = __pvclock_read_cycles(pvti-pvti, ret, flags);
/*
* Test we're still on the cpu as well as the version.
- * We could have been migrated just after the first
- * vgetcpu but before fetching the version, so we
- * wouldn't notice a version change.
+ * - We must read TSC of pvti's VCPU.
+ * - KVM doesn't follow the versioning protocol, so data could
+ * change before version if we left the VCPU.
*/
- cpu1 = __getcpu() VGETCPU_CPU_MASK;
- } while (unlikely(cpu != cpu1 ||
- (pvti-pvti.version 1) ||
+ smp_rmb();
+ } while (unlikely((pvti-pvti.version 1) ||
pvti-pvti.version != version ||
pvti-migrate_count != migrate_count));
--
2.3.4
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Reviewed-by: Marcelo Tosatti mtosa...@redhat.com
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Re: [PATCH] x86: vdso: fix pvclock races with task migration
On 04/02/2015 11:59 AM, Andy Lutomirski wrote:
On Thu, Apr 2, 2015 at 11:44 AM, Radim Krčmář rkrc...@redhat.com wrote:
If we were migrated right after __getcpu, but before reading the
migration_count, we wouldn't notice that we read TSC of a different
VCPU, nor that KVM's bug made pvti invalid, as only migration_count
on source VCPU is increased.
Change vdso instead of updating migration_count on destination.
Looks good to me.
Just to check: what tree is this intended to go through? I can take it,
but not until the previous patch makes it into Linus' tree or -tip. Or
I can take both patches.
Marcelo, Paolo?
--Andy
--Andy
Fixes: 0a4e6be9ca17 (x86: kvm: Revert remove sched notifier for cross-cpu
migrations)
Cc: sta...@vger.kernel.org
Signed-off-by: Radim Krčmář rkrc...@redhat.com
---
Because it we'll get a complete rewrite, this series does not
- remove the outdated 'TODO: We can put [...]' comment
- use a proper encapsulation for the inner do-while loop
- optimize the outer do-while loop
(no need to re-read cpu id on version mismatch)
arch/x86/vdso/vclock_gettime.c | 20
1 file changed, 12 insertions(+), 8 deletions(-)
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 30933760ee5f..40d2473836c9 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -99,21 +99,25 @@ static notrace cycle_t vread_pvclock(int *mode)
* __getcpu() calls (Gleb).
*/
- pvti = get_pvti(cpu);
+ /* Make sure migrate_count will change if we leave the VCPU. */
+ do {
+ pvti = get_pvti(cpu);
+ migrate_count = pvti-migrate_count;
- migrate_count = pvti-migrate_count;
+ cpu1 = cpu;
+ cpu = __getcpu() VGETCPU_CPU_MASK;
+ } while (unlikely(cpu != cpu1));
version = __pvclock_read_cycles(pvti-pvti, ret, flags);
/*
* Test we're still on the cpu as well as the version.
-* We could have been migrated just after the first
-* vgetcpu but before fetching the version, so we
-* wouldn't notice a version change.
+* - We must read TSC of pvti's VCPU.
+* - KVM doesn't follow the versioning protocol, so data could
+* change before version if we left the VCPU.
*/
- cpu1 = __getcpu() VGETCPU_CPU_MASK;
- } while (unlikely(cpu != cpu1 ||
- (pvti-pvti.version 1) ||
+ smp_rmb();
+ } while (unlikely((pvti-pvti.version 1) ||
pvti-pvti.version != version ||
pvti-migrate_count != migrate_count));
--
2.3.4
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Re: [PATCH] x86: vdso: fix pvclock races with task migration
On 06/04/2015 22:07, Andy Lutomirski wrote: On 04/02/2015 11:59 AM, Andy Lutomirski wrote: On Thu, Apr 2, 2015 at 11:44 AM, Radim Krčmář rkrc...@redhat.com wrote: If we were migrated right after __getcpu, but before reading the migration_count, we wouldn't notice that we read TSC of a different VCPU, nor that KVM's bug made pvti invalid, as only migration_count on source VCPU is increased. Change vdso instead of updating migration_count on destination. Looks good to me. Just to check: what tree is this intended to go through? I can take it, but not until the previous patch makes it into Linus' tree or -tip. Or I can take both patches. I'll take it for 4.1. Paolo -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] x86: vdso: fix pvclock races with task migration
On Thu, Apr 2, 2015 at 11:44 AM, Radim Krčmář rkrc...@redhat.com wrote:
If we were migrated right after __getcpu, but before reading the
migration_count, we wouldn't notice that we read TSC of a different
VCPU, nor that KVM's bug made pvti invalid, as only migration_count
on source VCPU is increased.
Change vdso instead of updating migration_count on destination.
Looks good to me.
--Andy
Fixes: 0a4e6be9ca17 (x86: kvm: Revert remove sched notifier for cross-cpu
migrations)
Cc: sta...@vger.kernel.org
Signed-off-by: Radim Krčmář rkrc...@redhat.com
---
Because it we'll get a complete rewrite, this series does not
- remove the outdated 'TODO: We can put [...]' comment
- use a proper encapsulation for the inner do-while loop
- optimize the outer do-while loop
(no need to re-read cpu id on version mismatch)
arch/x86/vdso/vclock_gettime.c | 20
1 file changed, 12 insertions(+), 8 deletions(-)
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 30933760ee5f..40d2473836c9 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -99,21 +99,25 @@ static notrace cycle_t vread_pvclock(int *mode)
* __getcpu() calls (Gleb).
*/
- pvti = get_pvti(cpu);
+ /* Make sure migrate_count will change if we leave the VCPU.
*/
+ do {
+ pvti = get_pvti(cpu);
+ migrate_count = pvti-migrate_count;
- migrate_count = pvti-migrate_count;
+ cpu1 = cpu;
+ cpu = __getcpu() VGETCPU_CPU_MASK;
+ } while (unlikely(cpu != cpu1));
version = __pvclock_read_cycles(pvti-pvti, ret, flags);
/*
* Test we're still on the cpu as well as the version.
-* We could have been migrated just after the first
-* vgetcpu but before fetching the version, so we
-* wouldn't notice a version change.
+* - We must read TSC of pvti's VCPU.
+* - KVM doesn't follow the versioning protocol, so data could
+* change before version if we left the VCPU.
*/
- cpu1 = __getcpu() VGETCPU_CPU_MASK;
- } while (unlikely(cpu != cpu1 ||
- (pvti-pvti.version 1) ||
+ smp_rmb();
+ } while (unlikely((pvti-pvti.version 1) ||
pvti-pvti.version != version ||
pvti-migrate_count != migrate_count));
--
2.3.4
--
Andy Lutomirski
AMA Capital Management, LLC
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[PATCH] x86: vdso: fix pvclock races with task migration
If we were migrated right after __getcpu, but before reading the
migration_count, we wouldn't notice that we read TSC of a different
VCPU, nor that KVM's bug made pvti invalid, as only migration_count
on source VCPU is increased.
Change vdso instead of updating migration_count on destination.
Fixes: 0a4e6be9ca17 (x86: kvm: Revert remove sched notifier for cross-cpu
migrations)
Cc: sta...@vger.kernel.org
Signed-off-by: Radim Krčmář rkrc...@redhat.com
---
Because it we'll get a complete rewrite, this series does not
- remove the outdated 'TODO: We can put [...]' comment
- use a proper encapsulation for the inner do-while loop
- optimize the outer do-while loop
(no need to re-read cpu id on version mismatch)
arch/x86/vdso/vclock_gettime.c | 20
1 file changed, 12 insertions(+), 8 deletions(-)
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 30933760ee5f..40d2473836c9 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -99,21 +99,25 @@ static notrace cycle_t vread_pvclock(int *mode)
* __getcpu() calls (Gleb).
*/
- pvti = get_pvti(cpu);
+ /* Make sure migrate_count will change if we leave the VCPU. */
+ do {
+ pvti = get_pvti(cpu);
+ migrate_count = pvti-migrate_count;
- migrate_count = pvti-migrate_count;
+ cpu1 = cpu;
+ cpu = __getcpu() VGETCPU_CPU_MASK;
+ } while (unlikely(cpu != cpu1));
version = __pvclock_read_cycles(pvti-pvti, ret, flags);
/*
* Test we're still on the cpu as well as the version.
-* We could have been migrated just after the first
-* vgetcpu but before fetching the version, so we
-* wouldn't notice a version change.
+* - We must read TSC of pvti's VCPU.
+* - KVM doesn't follow the versioning protocol, so data could
+* change before version if we left the VCPU.
*/
- cpu1 = __getcpu() VGETCPU_CPU_MASK;
- } while (unlikely(cpu != cpu1 ||
- (pvti-pvti.version 1) ||
+ smp_rmb();
+ } while (unlikely((pvti-pvti.version 1) ||
pvti-pvti.version != version ||
pvti-migrate_count != migrate_count));
--
2.3.4
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