diff options
| -rw-r--r-- | arch/x86/entry/vdso/vclock_gettime.c | 15 |
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; } |