提交 189e1173 编写于 作者: M Marcelo Tosatti

x86: pvclock: add note about rdtsc barriers

As noted by Gleb, not advertising SSE2 support implies
no RDTSC barriers.
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>
上级 2697902b
......@@ -74,6 +74,12 @@ unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
u8 ret_flags;
version = src->version;
/* Note: emulated platforms which do not advertise SSE2 support
* result in kvmclock not using the necessary RDTSC barriers.
* Without barriers, it is possible that RDTSC instruction reads from
* the time stamp counter outside rdtsc_barrier protected section
* below, resulting in violation of monotonicity.
*/
rdtsc_barrier();
offset = pvclock_get_nsec_offset(src);
ret = src->system_time + offset;
......
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