1 files changed, 8 insertions, 8 deletions

diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index c74436e687bf..72074d528400 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -85,15 +85,18 @@ static notrace cycle_t vread_pvclock(int *mode)
         cycle_t ret;
         u64 last;
         u32 version;
-        u32 migrate_count;
         u8 flags;
         unsigned cpu, cpu1;
 
 
         /*
-         * When looping to get a consistent (time-info, tsc) pair, we
-         * also need to deal with the possibility we can switch vcpus,
-         * so make sure we always re-fetch time-info for the current vcpu.
+         * Note: hypervisor must guarantee that:
+         * 1. cpu ID number maps 1:1 to per-CPU pvclock time info.
+         * 2. that per-CPU pvclock time info is updated if the
+         *    underlying CPU changes.
+         * 3. that version is increased whenever underlying CPU
+         *    changes.
+         *
          */
         do {
                 cpu = __getcpu() & VGETCPU_CPU_MASK;
@@ -104,8 +107,6 @@ static notrace cycle_t vread_pvclock(int *mode)
 
                 pvti = get_pvti(cpu);
 
-                migrate_count = pvti->migrate_count;
-
                 version = __pvclock_read_cycles(&pvti->pvti, &ret, &flags);
 
                 /*
@@ -117,8 +118,7 @@ static notrace cycle_t vread_pvclock(int *mode)
                 cpu1 = __getcpu() & VGETCPU_CPU_MASK;
         } while (unlikely(cpu != cpu1 ||
                           (pvti->pvti.version & 1) ||
-                          pvti->pvti.version != version ||
-                          pvti->migrate_count != migrate_count));
+                          pvti->pvti.version != version));
 
         if (unlikely(!(flags & PVCLOCK_TSC_STABLE_BIT)))
                 *mode = VCLOCK_NONE;