powerpc/perf: Exclude kernel samples while counting events in user space.

commit aa8e21c053d72b6639ea5a7f1d3a1d0209534c94 upstream.

Perf event attritube supports exclude_kernel flag to avoid
sampling/profiling in supervisor state (kernel). Based on this event
attr flag, Monitor Mode Control Register bit is set to freeze on
supervisor state. But sometimes (due to hardware limitation), Sampled
Instruction Address Register (SIAR) locks on to kernel address even
when freeze on supervisor is set. Patch here adds a check to drop
those samples.

Cc: stable@vger.kernel.org
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1606289215-1433-1-git-send-email-atrajeev@linux.vnet.ibm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 7bf1adcdfdaa119a7f0d5b502c9abb08d6f8329d..02fc75ddcbb36877a052791c46e10c9829cc7f14 100644 (file)
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -2089,6 +2089,16 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
        local64_set(&event->hw.period_left, left);
        perf_event_update_userpage(event);
 
+       /*
+        * Due to hardware limitation, sometimes SIAR could sample a kernel
+        * address even when freeze on supervisor state (kernel) is set in
+        * MMCR2. Check attr.exclude_kernel and address to drop the sample in
+        * these cases.
+        */
+       if (event->attr.exclude_kernel && record)
+               if (is_kernel_addr(mfspr(SPRN_SIAR)))
+                       record = 0;
+
        /*
         * Finally record data if requested.
         */