[PATCH 5.10 212/289] KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv_timer

From: Greg Kroah-Hartman
Date: Mon May 17 2021 - 12:01:44 EST

From: Wanpeng Li <wanpengli@xxxxxxxxxxx>

[ Upstream commit d981dd15498b188636ec5a7d8ad485e650f63d8d ]

Commit ee66e453db13d (KVM: lapic: Busy wait for timer to expire when
using hv_timer) tries to set ktime->expired_tscdeadline by checking
ktime->hv_timer_in_use since lapic timer oneshot/periodic modes which
are emulated by vmx preemption timer also get advanced, they leverage
the same vmx preemption timer logic with tsc-deadline mode. However,
ktime->hv_timer_in_use is cleared before apic_timer_expired() handling,
let's delay this clearing in preemption-disabled region.

Fixes: ee66e453db13d ("KVM: lapic: Busy wait for timer to expire when using hv_timer")
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
Message-Id: <1619608082-4187-1-git-send-email-wanpengli@xxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
arch/x86/kvm/lapic.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 4ca81ae9bc8a..5759eb075d2f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1908,8 +1908,8 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
if (!apic->lapic_timer.hv_timer_in_use)
goto out;
- cancel_hv_timer(apic);
apic_timer_expired(apic, false);
+ cancel_hv_timer(apic);

if (apic_lvtt_period(apic) && apic->lapic_timer.period) {