1 files changed, 13 insertions, 2 deletions

diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index 0f82a70c7682..4aed41f638bb 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -128,13 +128,24 @@ notrace static inline u64 vgetcyc(int mode)
 {
         if (mode == VCLOCK_TSC)
                 return (u64)rdtsc_ordered();
+
+        /*
+         * For any memory-mapped vclock type, we need to make sure that gcc
+         * doesn't cleverly hoist a load before the mode check.  Otherwise we
+         * might end up touching the memory-mapped page even if the vclock in
+         * question isn't enabled, which will segfault.  Hence the barriers.
+         */
 #ifdef CONFIG_PARAVIRT_CLOCK
-        else if (mode == VCLOCK_PVCLOCK)
+        if (mode == VCLOCK_PVCLOCK) {
+                barrier();
                 return vread_pvclock();
+        }
 #endif
 #ifdef CONFIG_HYPERV_TSCPAGE
-        else if (mode == VCLOCK_HVCLOCK)
+        if (mode == VCLOCK_HVCLOCK) {
+                barrier();
                 return vread_hvclock();
+        }
 #endif
         return U64_MAX;
 }