x86: kvm: Revert "remove sched notifier for cross-cpu migrations"
The following point:
2. per-CPU pvclock time info is updated if the
underlying CPU changes.
Is not true anymore since "KVM: x86: update pvclock area conditionally,
on cpu migration".
Add task migration notification back.
Problem noticed by Andy Lutomirski.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
CC: stable@kernel.org # 3.11+
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 9793322..3093376 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -82,18 +82,15 @@
cycle_t ret;
u64 last;
u32 version;
+ u32 migrate_count;
u8 flags;
unsigned cpu, cpu1;
/*
- * 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.
- *
+ * 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.
*/
do {
cpu = __getcpu() & VGETCPU_CPU_MASK;
@@ -104,6 +101,8 @@
pvti = get_pvti(cpu);
+ migrate_count = pvti->migrate_count;
+
version = __pvclock_read_cycles(&pvti->pvti, &ret, &flags);
/*
@@ -115,7 +114,8 @@
cpu1 = __getcpu() & VGETCPU_CPU_MASK;
} while (unlikely(cpu != cpu1 ||
(pvti->pvti.version & 1) ||
- pvti->pvti.version != version));
+ pvti->pvti.version != version ||
+ pvti->migrate_count != migrate_count));
if (unlikely(!(flags & PVCLOCK_TSC_STABLE_BIT)))
*mode = VCLOCK_NONE;