* [PATCH 0/2] x86/perf: A CR4.PCE bugfix and clarification @ 2017-03-16 19:59 Andy Lutomirski 2017-03-16 19:59 ` [PATCH 1/2] x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm Andy Lutomirski 2017-03-16 19:59 ` [PATCH 2/2] x86/perf: Clarify why x86_pmu_event_mapped() isn't racy Andy Lutomirski 0 siblings, 2 replies; 5+ messages in thread From: Andy Lutomirski @ 2017-03-16 19:59 UTC (permalink / raw) To: X86 ML; +Cc: linux-kernel, Borislav Petkov, Vince Weaver, Andy Lutomirski Hi all- Vince found a bug in our CR4.PCE handling. While investigating, I found what looked like another bug but actually wasn't. Here's a fix for the bug (cc'd to stable) and a comment and lockdep annotation for why the other non-bug isn't actually a bug. Andy Lutomirski (2): x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm x86/perf: Clarify why x86_pmu_event_mapped() isn't racy arch/x86/events/core.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) -- 2.9.3 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH 1/2] x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm 2017-03-16 19:59 [PATCH 0/2] x86/perf: A CR4.PCE bugfix and clarification Andy Lutomirski @ 2017-03-16 19:59 ` Andy Lutomirski 2017-03-17 10:16 ` [tip:perf/urgent] " tip-bot for Andy Lutomirski 2017-03-16 19:59 ` [PATCH 2/2] x86/perf: Clarify why x86_pmu_event_mapped() isn't racy Andy Lutomirski 1 sibling, 1 reply; 5+ messages in thread From: Andy Lutomirski @ 2017-03-16 19:59 UTC (permalink / raw) To: X86 ML Cc: linux-kernel, Borislav Petkov, Vince Weaver, Andy Lutomirski, stable If one thread mmaps a perf event while another thread in the same mm is in some context where active_mm != mm (which can happen in the scheduler, for example), refresh_pce() would write the wrong value to CR4.PCE. This broke some PAPI tests. Cc: stable@vger.kernel.org Fixes: 7911d3f7af14 ("perf/x86: Only allow rdpmc if a perf_event is mapped") Reported-and-tested-by: Vince Weaver <vincent.weaver@maine.edu> Signed-off-by: Andy Lutomirski <luto@kernel.org> --- arch/x86/events/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 349d4d17aa7f..4f564df73b8f 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2101,8 +2101,8 @@ static int x86_pmu_event_init(struct perf_event *event) static void refresh_pce(void *ignored) { - if (current->mm) - load_mm_cr4(current->mm); + if (current->active_mm) + load_mm_cr4(current->active_mm); } static void x86_pmu_event_mapped(struct perf_event *event) -- 2.9.3 ^ permalink raw reply related [flat|nested] 5+ messages in thread
* [tip:perf/urgent] x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm 2017-03-16 19:59 ` [PATCH 1/2] x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm Andy Lutomirski @ 2017-03-17 10:16 ` tip-bot for Andy Lutomirski 0 siblings, 0 replies; 5+ messages in thread From: tip-bot for Andy Lutomirski @ 2017-03-17 10:16 UTC (permalink / raw) To: linux-tip-commits Cc: luto, mingo, acme, vincent.weaver, eranian, hpa, peterz, alexander.shishkin, torvalds, tglx, bpetkov, linux-kernel, jolsa Commit-ID: 5dc855d44c2ad960a86f593c60461f1ae1566b6d Gitweb: http://git.kernel.org/tip/5dc855d44c2ad960a86f593c60461f1ae1566b6d Author: Andy Lutomirski <luto@kernel.org> AuthorDate: Thu, 16 Mar 2017 12:59:39 -0700 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Fri, 17 Mar 2017 08:28:26 +0100 x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm If one thread mmaps a perf event while another thread in the same mm is in some context where active_mm != mm (which can happen in the scheduler, for example), refresh_pce() would write the wrong value to CR4.PCE. This broke some PAPI tests. Reported-and-tested-by: Vince Weaver <vincent.weaver@maine.edu> Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Borislav Petkov <bpetkov@suse.de> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org Fixes: 7911d3f7af14 ("perf/x86: Only allow rdpmc if a perf_event is mapped") Link: http://lkml.kernel.org/r/0c5b38a76ea50e405f9abe07a13dfaef87c173a1.1489694270.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/events/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 1635c0c..e07b36c 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2100,8 +2100,8 @@ static int x86_pmu_event_init(struct perf_event *event) static void refresh_pce(void *ignored) { - if (current->mm) - load_mm_cr4(current->mm); + if (current->active_mm) + load_mm_cr4(current->active_mm); } static void x86_pmu_event_mapped(struct perf_event *event) ^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH 2/2] x86/perf: Clarify why x86_pmu_event_mapped() isn't racy 2017-03-16 19:59 [PATCH 0/2] x86/perf: A CR4.PCE bugfix and clarification Andy Lutomirski 2017-03-16 19:59 ` [PATCH 1/2] x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm Andy Lutomirski @ 2017-03-16 19:59 ` Andy Lutomirski 2017-03-17 10:17 ` [tip:perf/urgent] " tip-bot for Andy Lutomirski 1 sibling, 1 reply; 5+ messages in thread From: Andy Lutomirski @ 2017-03-16 19:59 UTC (permalink / raw) To: X86 ML; +Cc: linux-kernel, Borislav Petkov, Vince Weaver, Andy Lutomirski Naively, it looks racy, but mmap_sem saves it. Add a comment and a lockdep assertion. Signed-off-by: Andy Lutomirski <luto@kernel.org> --- arch/x86/events/core.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 4f564df73b8f..2aa1ad194db2 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2110,6 +2110,18 @@ static void x86_pmu_event_mapped(struct perf_event *event) if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED)) return; + /* + * This function relies on not being called concurrently in two + * tasks in the same mm. Otherwise one task could observe + * perf_rdpmc_allowed > 1 and return all the way back to + * userspace with CR4.PCE clear while another task is still + * doing on_each_cpu_mask() to propagate CR4.PCE. + * + * For now, this can't happen because all callers hold mmap_sem + * for write. If this changes, we'll need a different solution. + */ + lockdep_assert_held_exclusive(¤t->mm->mmap_sem); + if (atomic_inc_return(¤t->mm->context.perf_rdpmc_allowed) == 1) on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1); } -- 2.9.3 ^ permalink raw reply related [flat|nested] 5+ messages in thread
* [tip:perf/urgent] x86/perf: Clarify why x86_pmu_event_mapped() isn't racy 2017-03-16 19:59 ` [PATCH 2/2] x86/perf: Clarify why x86_pmu_event_mapped() isn't racy Andy Lutomirski @ 2017-03-17 10:17 ` tip-bot for Andy Lutomirski 0 siblings, 0 replies; 5+ messages in thread From: tip-bot for Andy Lutomirski @ 2017-03-17 10:17 UTC (permalink / raw) To: linux-tip-commits Cc: torvalds, alexander.shishkin, linux-kernel, bpetkov, luto, tglx, vincent.weaver, eranian, jolsa, hpa, mingo, peterz, acme Commit-ID: 4b07372a32c0c1505a7634ad7e607d83340ef645 Gitweb: http://git.kernel.org/tip/4b07372a32c0c1505a7634ad7e607d83340ef645 Author: Andy Lutomirski <luto@kernel.org> AuthorDate: Thu, 16 Mar 2017 12:59:40 -0700 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Fri, 17 Mar 2017 08:28:26 +0100 x86/perf: Clarify why x86_pmu_event_mapped() isn't racy Naively, it looks racy, but ->mmap_sem saves it. Add a comment and a lockdep assertion. Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Borislav Petkov <bpetkov@suse.de> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vince Weaver <vincent.weaver@maine.edu> Link: http://lkml.kernel.org/r/03a1e629063899168dfc4707f3bb6e581e21f5c6.1489694270.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/events/core.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index e07b36c..183a972 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2109,6 +2109,18 @@ static void x86_pmu_event_mapped(struct perf_event *event) if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED)) return; + /* + * This function relies on not being called concurrently in two + * tasks in the same mm. Otherwise one task could observe + * perf_rdpmc_allowed > 1 and return all the way back to + * userspace with CR4.PCE clear while another task is still + * doing on_each_cpu_mask() to propagate CR4.PCE. + * + * For now, this can't happen because all callers hold mmap_sem + * for write. If this changes, we'll need a different solution. + */ + lockdep_assert_held_exclusive(¤t->mm->mmap_sem); + if (atomic_inc_return(¤t->mm->context.perf_rdpmc_allowed) == 1) on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1); } ^ permalink raw reply related [flat|nested] 5+ messages in thread
end of thread, other threads:[~2017-03-17 10:43 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2017-03-16 19:59 [PATCH 0/2] x86/perf: A CR4.PCE bugfix and clarification Andy Lutomirski 2017-03-16 19:59 ` [PATCH 1/2] x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm Andy Lutomirski 2017-03-17 10:16 ` [tip:perf/urgent] " tip-bot for Andy Lutomirski 2017-03-16 19:59 ` [PATCH 2/2] x86/perf: Clarify why x86_pmu_event_mapped() isn't racy Andy Lutomirski 2017-03-17 10:17 ` [tip:perf/urgent] " tip-bot for Andy Lutomirski
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