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-rw-r--r--arch/x86/entry/vdso/vclock_gettime.c15
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;
}