1 files changed, 23 insertions, 1 deletions

diff --git a/arch/powerpc/oprofile/op_model_power4.c b/arch/powerpc/oprofile/op_model_power4.c
index 8ee51a252cf1..e6bec74be131 100644
--- a/arch/powerpc/oprofile/op_model_power4.c
+++ b/arch/powerpc/oprofile/op_model_power4.c
@@ -261,6 +261,28 @@ static int get_kernel(unsigned long pc, unsigned long mmcra)
         return is_kernel;
 }
 
+static bool pmc_overflow(unsigned long val)
+{
+        if ((int)val < 0)
+                return true;
+
+        /*
+         * Events on POWER7 can roll back if a speculative event doesn't
+         * eventually complete. Unfortunately in some rare cases they will
+         * raise a performance monitor exception. We need to catch this to
+         * ensure we reset the PMC. In all cases the PMC will be 256 or less
+         * cycles from overflow.
+         *
+         * We only do this if the first pass fails to find any overflowing
+         * PMCs because a user might set a period of less than 256 and we
+         * don't want to mistakenly reset them.
+         */
+        if (__is_processor(PV_POWER7) && ((0x80000000 - val) <= 256))
+                return true;
+
+        return false;
+}
+
 static void power4_handle_interrupt(struct pt_regs *regs,
                                     struct op_counter_config *ctr)
 {
@@ -281,7 +303,7 @@ static void power4_handle_interrupt(struct pt_regs *regs,
 
         for (i = 0; i < cur_cpu_spec->num_pmcs; ++i) {
                 val = classic_ctr_read(i);
-                if (val < 0) {
+                if (pmc_overflow(val)) {
                         if (oprofile_running && ctr[i].enabled) {
                                 oprofile_add_ext_sample(pc, regs, i, is_kernel);
                                 classic_ctr_write(i, reset_value[i]);