Validity of values returned by pvclock (including flags) is guaranteed by version checks.
That is, read of src->flags outside version check protection can refer to a different paravirt clock update by the hypervisor. Signed-off-by: Marcelo Tosatti <[email protected]> Index: vsyscall/arch/x86/include/asm/pvclock.h =================================================================== --- vsyscall.orig/arch/x86/include/asm/pvclock.h +++ vsyscall/arch/x86/include/asm/pvclock.h @@ -66,18 +66,21 @@ u64 pvclock_get_nsec_offset(const struct static __always_inline unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src, - cycle_t *cycles) + cycle_t *cycles, u8 *flags) { unsigned version; cycle_t ret, offset; + u8 ret_flags; version = src->version; rdtsc_barrier(); offset = pvclock_get_nsec_offset(src); ret = src->system_time + offset; + ret_flags = src->flags; rdtsc_barrier(); *cycles = ret; + *flags = ret_flags; return version; } Index: vsyscall/arch/x86/kernel/pvclock.c =================================================================== --- vsyscall.orig/arch/x86/kernel/pvclock.c +++ vsyscall/arch/x86/kernel/pvclock.c @@ -50,13 +50,14 @@ cycle_t pvclock_clocksource_read(struct unsigned version; cycle_t ret; u64 last; + u8 flags; do { - version = __pvclock_read_cycles(src, &ret); + version = __pvclock_read_cycles(src, &ret, &flags); } while ((src->version & 1) || version != src->version); if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) && - (src->flags & PVCLOCK_TSC_STABLE_BIT)) + (flags & PVCLOCK_TSC_STABLE_BIT)) return ret; /* -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
