[PATCH v5 02/33] KVM: x86: Purge "highest ISR" cache when updating APICv state

Sean Christopherson
2023-01-06T01:13:48Z

Purge the "highest ISR" cache when updating APICv state on a vCPU. The
cache must not be used when APICv is active as hardware may emulate EOIs
(and other operations) without exiting to KVM.

This fixes a bug where KVM will effectively block IRQs in perpetuity due
to the "highest ISR" never getting reset if APICv is activated on a vCPU
while an IRQ is in-service. Hardware emulates the EOI and KVM never gets
a chance to update its cache.

Fixes: b26a695a1d78 ("kvm: lapic: Introduce APICv update helper function")
Cc: stable@vger.kernel.org
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/lapic.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 5c0f93fc073a..33a661d82da7 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2424,6 +2424,7 @@ void kvm_apic_update_apicv(struct kvm_vcpu *vcpu)
*/
apic->isr_count = count_vectors(apic->regs + APIC_ISR);
}
+ apic->highest_isr_cache = -1;
}

void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
@@ -2479,7 +2480,6 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
kvm_lapic_set_reg(apic, APIC_TMR + 0x10 * i, 0);
}
kvm_apic_update_apicv(vcpu);
- apic->highest_isr_cache = -1;
update_divide_count(apic);
atomic_set(&apic->lapic_timer.pending, 0);

@@ -2767,7 +2767,6 @@ int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)
__start_apic_timer(apic, APIC_TMCCT);
kvm_lapic_set_reg(apic, APIC_TMCCT, 0);
kvm_apic_update_apicv(vcpu);
- apic->highest_isr_cache = -1;
if (apic->apicv_active) {
static_call_cond(kvm_x86_apicv_post_state_restore)(vcpu);
static_call_cond(kvm_x86_hwapic_irr_update)(vcpu, apic_find_highest_irr(apic));
--
2.39.0.314.g84b9a713c41-goog