2 files changed, 13 insertions, 2 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 69b84a26ea17..c7c4d9c51e99 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -259,6 +259,17 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
         clocks_calc_mult_shift(&data->cyc2ns_mul, &data->cyc2ns_shift, cpu_khz,
                                NSEC_PER_MSEC, 0);
 
+        /*
+         * cyc2ns_shift is exported via arch_perf_update_userpage() where it is
+         * not expected to be greater than 31 due to the original published
+         * conversion algorithm shifting a 32-bit value (now specifies a 64-bit
+         * value) - refer perf_event_mmap_page documentation in perf_event.h.
+         */
+        if (data->cyc2ns_shift == 32) {
+                data->cyc2ns_shift = 31;
+                data->cyc2ns_mul >>= 1;
+        }
+
         data->cyc2ns_offset = ns_now -
                 mul_u64_u32_shr(tsc_now, data->cyc2ns_mul, data->cyc2ns_shift);
 
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 2881145cda86..6c72e72e975c 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -476,7 +476,7 @@ struct perf_event_mmap_page {
          *   u64 delta;
          *
          *   quot = (cyc >> time_shift);
-         *   rem = cyc & ((1 << time_shift) - 1);
+         *   rem = cyc & (((u64)1 << time_shift) - 1);
          *   delta = time_offset + quot * time_mult +
          *              ((rem * time_mult) >> time_shift);
          *
@@ -507,7 +507,7 @@ struct perf_event_mmap_page {
          * And vice versa:
          *
          *   quot = cyc >> time_shift;
-         *   rem  = cyc & ((1 << time_shift) - 1);
+         *   rem  = cyc & (((u64)1 << time_shift) - 1);
          *   timestamp = time_zero + quot * time_mult +
          *               ((rem * time_mult) >> time_shift);
          */