When a virtual machine uses the HV timer during suspend, the KVM timer does
not advance. Upon waking after a long period, there may be a significant
gap between target_expiration and the current time. Since each timer
expiration only advances target_expiration by one period, the expiration
handler can be invoked repeatedly to catch up.
Additionally, if the advanced target_expiration remained less than the
current time, tscdeadline could be set to a negative value. This would
cause HV timer setup to fail and fallback to the SW timer. After switching
to SW timer, apic_timer_fn could be repeatedly executed within a single
clock interrupt handler, resulting in a hardlockup:
NMI watchdog: Watchdog detected hard LOCKUP on cpu 45
...
RIP: 0010:advance_periodic_target_expiration+0x4d/0x80 [kvm]
...
RSP: 0018:ff4f88f5d98d8ef0 EFLAGS: 00000046
RAX: fff0103f91be678e RBX: fff0103f91be678e RCX: 00843a7d9e127bcc
RDX: 0000000000000002 RSI: 0052ca4003697505 RDI: ff440d5bfbdbd500
RBP: ff440d5956f99200 R08: ff2ff2a42deb6a84 R09: 000000000002a6c0
R10: 0122d794016332b3 R11: 0000000000000000 R12: ff440db1af39cfc0
R13: ff440db1af39cfc0 R14: ffffffffc0d4a560 R15: ff440db1af39d0f8
FS: 00007f04a6ffd700(0000) GS:ff440db1af380000(0000) knlGS:000000e38a3b8000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000d5651feff8 CR3: 000000684e038002 CR4: 0000000000773ee0
PKRU: 55555554
Call Trace:
apic_timer_fn+0x31/0x50 [kvm]
__hrtimer_run_queues+0x100/0x280
hrtimer_interrupt+0x100/0x210
? ttwu_do_wakeup+0x19/0x160
smp_apic_timer_interrupt+0x6a/0x130
apic_timer_interrupt+0xf/0x20
We modify it as follows: if, after advancing, after advancing,
target_expiration is still less than the current time, we set
target_expiration directly to now. This also ensures that delta is
non-negative.
Fixes: d8f2f498d9ed ("x86/kvm: fix LAPIC timer drift when guest uses periodic mode")
Signed-off-by: fuqiang wang
---
arch/x86/kvm/lapic.c | 32 ++++++++++++++++++++++++--------
1 file changed, 24 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0ae7f913d782..307e2d6c3450 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2131,18 +2131,34 @@ static void advance_periodic_target_expiration(struct kvm_lapic *apic)
ktime_t delta;
/*
- * Synchronize both deadlines to the same time source or
- * differences in the periods (caused by differences in the
- * underlying clocks or numerical approximation errors) will
- * cause the two to drift apart over time as the errors
- * accumulate.
+ * Use kernel time as the time source for both deadlines so that they
+ * stay synchronized. Computing each deadline independently will cause
+ * the two deadlines to drift apart over time as differences in the
+ * periods accumulate, e.g. due to differences in the underlying clocks
+ * or numerical approximation errors.
*/
apic->lapic_timer.target_expiration =
ktime_add_ns(apic->lapic_timer.target_expiration,
apic->lapic_timer.period);
+
+ /*
+ * When the vm is suspend, the hv timer also stops advancing. After it
+ * is resumed, this may result in a large delta. If the
+ * target_expiration only advances by one period each time, it will
+ * cause KVM to frequently handle timer expirations.
+ */
+ if (apic->lapic_timer.period > 0 &&
+ ktime_before(apic->lapic_timer.target_expiration, now))
+ apic->lapic_timer.target_expiration = now;
+
delta = ktime_sub(apic->lapic_timer.target_expiration, now);
- apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, tscl) +
- nsec_to_cycles(apic->vcpu, delta);
+ apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, tscl);
+ /*
+ * Note: delta must not be negative. Otherwise, blindly adding a
+ * negative delta could cause the deadline to become excessively large
+ * due to the deadline being an unsigned value.
+ */
+ apic->lapic_timer.tscdeadline += nsec_to_cycles(apic->vcpu, delta);
}
static void start_sw_period(struct kvm_lapic *apic)
@@ -2972,7 +2988,7 @@ static enum hrtimer_restart apic_timer_fn(struct hrtimer *data)
if (lapic_is_periodic(apic)) {
advance_periodic_target_expiration(apic);
- hrtimer_add_expires_ns(&ktimer->timer, ktimer->period);
+ hrtimer_set_expires(&ktimer->timer, ktimer->target_expiration);
return HRTIMER_RESTART;
} else
return HRTIMER_NORESTART;
--
2.47.0