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Two perf events fixes: 

- Fix mmap_count warning & bug when creating a group member event
    with the PERF_FLAG_FD_OUTPUT flag.
 
  - Disable the sample period == 1 branch events BTS optimization
    on guests, because BTS is not virtualized.
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'perf-urgent-2026-01-24' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull perf events fixes from Ingo Molnar:

 - Fix mmap_count warning & bug when creating a group member event
   with the PERF_FLAG_FD_OUTPUT flag

 - Disable the sample period == 1 branch events BTS optimization
   on guests, because BTS is not virtualized

* tag 'perf-urgent-2026-01-24' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf/x86/intel: Do not enable BTS for guests
  perf: Fix refcount warning on event->mmap_count increment
master
Linus Torvalds 2026-01-24 09:24:17 -08:00
parent dc67a35505 91dcfae0ff
commit ceaeaf66a2
2 changed files with 20 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
arch/x86/events/perf_event.h
View File

@ -1574,13 +1574,22 @@ static inline bool intel_pmu_has_bts_period(struct perf_event *event, u64 period
struct hw_perf_event *hwc = &event->hw;
unsigned int hw_event, bts_event;
if (event->attr.freq)
/*
* Only use BTS for fixed rate period==1 events.
*/
if (event->attr.freq || period != 1)
return false;
/*
* BTS doesn't virtualize.
*/
if (event->attr.exclude_host)
return false;
hw_event = hwc->config & INTEL_ARCH_EVENT_MASK;
bts_event = x86_pmu.event_map(PERF_COUNT_HW_BRANCH_INSTRUCTIONS);
return hw_event == bts_event && period == 1;
return hw_event == bts_event;
}
static inline bool intel_pmu_has_bts(struct perf_event *event)

9
kernel/events/core.c
View File

@ -6997,6 +6997,15 @@ static int perf_mmap_rb(struct vm_area_struct *vma, struct perf_event *event,
if (data_page_nr(event->rb) != nr_pages)
return -EINVAL;
/*
* If this event doesn't have mmap_count, we're attempting to
* create an alias of another event's mmap(); this would mean
* both events will end up scribbling the same user_page;
* which makes no sense.
*/
if (!refcount_read(&event->mmap_count))
return -EBUSY;
if (refcount_inc_not_zero(&event->rb->mmap_count)) {
/*
* Success -- managed to mmap() the same buffer