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perf/core: Disable page faults when getting phys address
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We hit following warning when running tests on kernel
compiled with CONFIG_DEBUG_ATOMIC_SLEEP=y:

 WARNING: CPU: 19 PID: 4472 at mm/gup.c:2381 __get_user_pages_fast+0x1a4/0x200
 CPU: 19 PID: 4472 Comm: dummy Not tainted 5.6.0-rc6+ #3
 RIP: 0010:__get_user_pages_fast+0x1a4/0x200
 ...
 Call Trace:
  perf_prepare_sample+0xff1/0x1d90
  perf_event_output_forward+0xe8/0x210
  __perf_event_overflow+0x11a/0x310
  __intel_pmu_pebs_event+0x657/0x850
  intel_pmu_drain_pebs_nhm+0x7de/0x11d0
  handle_pmi_common+0x1b2/0x650
  intel_pmu_handle_irq+0x17b/0x370
  perf_event_nmi_handler+0x40/0x60
  nmi_handle+0x192/0x590
  default_do_nmi+0x6d/0x150
  do_nmi+0x2f9/0x3c0
  nmi+0x8e/0xd7

While __get_user_pages_fast() is IRQ-safe, it calls access_ok(),
which warns on:

  WARN_ON_ONCE(!in_task() && !pagefault_disabled())

Peter suggested disabling page faults around __get_user_pages_fast(),
which gets rid of the warning in access_ok() call.

Suggested-by: Peter Zijlstra <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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olsajiri authored and Ingo Molnar committed Apr 8, 2020
1 parent 2b3b76b commit d3296fb
Showing 1 changed file with 6 additions and 3 deletions.
9 changes: 6 additions & 3 deletions kernel/events/core.c
Original file line number Diff line number Diff line change
Expand Up @@ -6934,9 +6934,12 @@ static u64 perf_virt_to_phys(u64 virt)
* Try IRQ-safe __get_user_pages_fast first.
* If failed, leave phys_addr as 0.
*/
if ((current->mm != NULL) &&
(__get_user_pages_fast(virt, 1, 0, &p) == 1))
phys_addr = page_to_phys(p) + virt % PAGE_SIZE;
if (current->mm != NULL) {
pagefault_disable();
if (__get_user_pages_fast(virt, 1, 0, &p) == 1)
phys_addr = page_to_phys(p) + virt % PAGE_SIZE;
pagefault_enable();
}

if (p)
put_page(p);
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