[PATCH 3/4] KVM: x86: check PIR even for vCPUs with disabled APICv

Paolo Bonzini
2021-11-23T00:43:34Z

The IRTE for an assigned device can trigger a POSTED_INTR_VECTOR even
if APICv is disabled on the vCPU that receives it. In that case, the
interrupt will just cause a vmexit and leave the ON bit set together
with the PIR bit corresponding to the interrupt.

Right now, the interrupt would not be delivered until APICv is re-enabled.
However, fixing this is just a matter of always doing the PIR->IRR
synchronization, even if the vCPU has temporarily disabled APICv.

This is not a problem for performance, or if anything it is an
improvement. First, in the common case where vcpu->arch.apicv_active is
true, one fewer check has to be performed. Second, static_call_cond will
elide the function call if APICv is not present or disabled. Finally,
in the case for AMD hardware we can remove the sync_pir_to_irr callback:
it is only needed for apic_has_interrupt_for_ppr, and that function
already has a fallback for !APICv.

Cc: stable@vger.kernel.org
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/lapic.c | 2 +-
arch/x86/kvm/svm/svm.c | 1 -
arch/x86/kvm/x86.c | 18 +++++++++---------
3 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 759952dd1222..f206fc35deff 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -707,7 +707,7 @@ static void pv_eoi_clr_pending(struct kvm_vcpu *vcpu)
static int apic_has_interrupt_for_ppr(struct kvm_lapic *apic, u32 ppr)
{
int highest_irr;
- if (apic->vcpu->arch.apicv_active)
+ if (kvm_x86_ops.sync_pir_to_irr)
highest_irr = static_call(kvm_x86_sync_pir_to_irr)(apic->vcpu);
else
highest_irr = apic_find_highest_irr(apic);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 5630c241d5f6..d0f68d11ec70 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4651,7 +4651,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
.load_eoi_exitmap = svm_load_eoi_exitmap,
.hwapic_irr_update = svm_hwapic_irr_update,
.hwapic_isr_update = svm_hwapic_isr_update,
- .sync_pir_to_irr = kvm_lapic_find_highest_irr,
.apicv_post_state_restore = avic_post_state_restore,

.set_tss_addr = svm_set_tss_addr,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 441f4769173e..a8f12c83db4b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4448,8 +4448,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu,
struct kvm_lapic_state *s)
{
- if (vcpu->arch.apicv_active)
- static_call(kvm_x86_sync_pir_to_irr)(vcpu);
+ static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);

return kvm_apic_get_state(vcpu, s);
}
@@ -9528,8 +9527,7 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
if (irqchip_split(vcpu->kvm))
kvm_scan_ioapic_routes(vcpu, vcpu->arch.ioapic_handled_vectors);
else {
- if (vcpu->arch.apicv_active)
- static_call(kvm_x86_sync_pir_to_irr)(vcpu);
+ static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);
if (ioapic_in_kernel(vcpu->kvm))
kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
}
@@ -9802,10 +9800,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)

/*
* This handles the case where a posted interrupt was
- * notified with kvm_vcpu_kick.
+ * notified with kvm_vcpu_kick. Assigned devices can
+ * use the POSTED_INTR_VECTOR even if APICv is disabled,
+ * so do it even if APICv is disabled on this vCPU.
*/
- if (kvm_lapic_enabled(vcpu) && vcpu->arch.apicv_active)
- static_call(kvm_x86_sync_pir_to_irr)(vcpu);
+ if (kvm_lapic_enabled(vcpu))
+ static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);

if (kvm_vcpu_exit_request(vcpu)) {
vcpu->mode = OUTSIDE_GUEST_MODE;
@@ -9849,8 +9849,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
if (likely(exit_fastpath != EXIT_FASTPATH_REENTER_GUEST))
break;

- if (kvm_lapic_enabled(vcpu) && vcpu->arch.apicv_active)
- static_call(kvm_x86_sync_pir_to_irr)(vcpu);
+ if (kvm_lapic_enabled(vcpu))
+ static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);

if (unlikely(kvm_vcpu_exit_request(vcpu))) {
exit_fastpath = EXIT_FASTPATH_EXIT_HANDLED;
--
2.27.0