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Subject[PATCH 4.12 28/41] perf/x86: Fix RDPMC vs. mm_struct tracking
Date
4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@infradead.org>

commit bfe334924ccd9f4a53f30240c03cf2f43f5b2df1 upstream.

Vince reported the following rdpmc() testcase failure:

> Failing test case:
>
> fd=perf_event_open();
> addr=mmap(fd);
> exec() // without closing or unmapping the event
> fd=perf_event_open();
> addr=mmap(fd);
> rdpmc() // GPFs due to rdpmc being disabled

The problem is of course that exec() plays tricks with what is
current->mm, only destroying the old mappings after having
installed the new mm.

Fix this confusion by passing along vma->vm_mm instead of relying on
current->mm.

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Tested-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 1e0fb9ec679c ("perf: Add pmu callbacks to track event mapping and unmapping")
Link: http://lkml.kernel.org/r/20170802173930.cstykcqefmqt7jau@hirez.programming.kicks-ass.net
[ Minor cleanups. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/events/core.c | 16 +++++++---------
include/linux/perf_event.h | 4 ++--
kernel/events/core.c | 6 +++---
3 files changed, 12 insertions(+), 14 deletions(-)

--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2105,7 +2105,7 @@ static void refresh_pce(void *ignored)
load_mm_cr4(current->active_mm);
}

-static void x86_pmu_event_mapped(struct perf_event *event)
+static void x86_pmu_event_mapped(struct perf_event *event, struct mm_struct *mm)
{
if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED))
return;
@@ -2120,22 +2120,20 @@ static void x86_pmu_event_mapped(struct
* 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(&current->mm->mmap_sem);
+ lockdep_assert_held_exclusive(&mm->mmap_sem);

- if (atomic_inc_return(&current->mm->context.perf_rdpmc_allowed) == 1)
- on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1);
+ if (atomic_inc_return(&mm->context.perf_rdpmc_allowed) == 1)
+ on_each_cpu_mask(mm_cpumask(mm), refresh_pce, NULL, 1);
}

-static void x86_pmu_event_unmapped(struct perf_event *event)
+static void x86_pmu_event_unmapped(struct perf_event *event, struct mm_struct *mm)
{
- if (!current->mm)
- return;

if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED))
return;

- if (atomic_dec_and_test(&current->mm->context.perf_rdpmc_allowed))
- on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1);
+ if (atomic_dec_and_test(&mm->context.perf_rdpmc_allowed))
+ on_each_cpu_mask(mm_cpumask(mm), refresh_pce, NULL, 1);
}

static int x86_pmu_event_idx(struct perf_event *event)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -310,8 +310,8 @@ struct pmu {
* Notification that the event was mapped or unmapped. Called
* in the context of the mapping task.
*/
- void (*event_mapped) (struct perf_event *event); /*optional*/
- void (*event_unmapped) (struct perf_event *event); /*optional*/
+ void (*event_mapped) (struct perf_event *event, struct mm_struct *mm); /* optional */
+ void (*event_unmapped) (struct perf_event *event, struct mm_struct *mm); /* optional */

/*
* Flags for ->add()/->del()/ ->start()/->stop(). There are
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5084,7 +5084,7 @@ static void perf_mmap_open(struct vm_are
atomic_inc(&event->rb->aux_mmap_count);

if (event->pmu->event_mapped)
- event->pmu->event_mapped(event);
+ event->pmu->event_mapped(event, vma->vm_mm);
}

static void perf_pmu_output_stop(struct perf_event *event);
@@ -5107,7 +5107,7 @@ static void perf_mmap_close(struct vm_ar
unsigned long size = perf_data_size(rb);

if (event->pmu->event_unmapped)
- event->pmu->event_unmapped(event);
+ event->pmu->event_unmapped(event, vma->vm_mm);

/*
* rb->aux_mmap_count will always drop before rb->mmap_count and
@@ -5405,7 +5405,7 @@ aux_unlock:
vma->vm_ops = &perf_mmap_vmops;

if (event->pmu->event_mapped)
- event->pmu->event_mapped(event);
+ event->pmu->event_mapped(event, vma->vm_mm);

return ret;
}

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