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 <mtosatti@xxxxxxxxxx>
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;
/*
--
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