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KVM: SVM: fix race between interrupt delivery and AVIC inhibition 

If svm_deliver_avic_intr is called just after the target vcpu's AVIC got
inhibited, it might read a stale value of vcpu->arch.apicv_active
which can lead to the target vCPU not noticing the interrupt.

To fix this use load-acquire/store-release so that, if the target vCPU
is IN_GUEST_MODE, we're guaranteed to see a previous disabling of the
AVIC.  If AVIC has been disabled in the meanwhile, proceed with the
KVM_REQ_EVENT-based delivery.

Incomplete IPI vmexit has the same races as svm_deliver_avic_intr, and
in fact it can be handled in exactly the same way; the only difference
lies in who has set IRR, whether svm_deliver_interrupt or the processor.
Therefore, svm_complete_interrupt_delivery can be used to fix incomplete
IPI vmexits as well.

Co-developed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Maxim Levitsky 2022-02-08 06:48:42 -05:00 committed by Paolo Bonzini
parent 30811174f0
commit 66fa226c13
4 changed files with 56 additions and 50 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
arch/x86/kvm/svm/avic.c
View File

@ -269,7 +269,7 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu)
return 0;
}
static void avic_ring_doorbell(struct kvm_vcpu *vcpu)
void avic_ring_doorbell(struct kvm_vcpu *vcpu)
{
/*
* Note, the vCPU could get migrated to a different pCPU at any point,
@ -300,8 +300,13 @@ static void avic_kick_target_vcpus(struct kvm *kvm, struct kvm_lapic *source,
kvm_for_each_vcpu(i, vcpu, kvm) {
if (kvm_apic_match_dest(vcpu, source, icrl & APIC_SHORT_MASK,
GET_APIC_DEST_FIELD(icrh),
icrl & APIC_DEST_MASK))
kvm_vcpu_wake_up(vcpu);
icrl & APIC_DEST_MASK)) {
vcpu->arch.apic->irr_pending = true;
svm_complete_interrupt_delivery(vcpu,
icrl & APIC_MODE_MASK,
icrl & APIC_INT_LEVELTRIG,
icrl & APIC_VECTOR_MASK);
}
}
}
@ -663,43 +668,6 @@ void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
return;
}
int svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec)
{
if (!vcpu->arch.apicv_active)
return -1;
/*
* Pairs with the smp_mb_*() after setting vcpu->guest_mode in
* vcpu_enter_guest() to ensure the write to the vIRR is ordered before
* the read of guest_mode, which guarantees that either VMRUN will see
* and process the new vIRR entry, or that the below code will signal
* the doorbell if the vCPU is already running in the guest.
*/
smp_mb__after_atomic();
/*
* Signal the doorbell to tell hardware to inject the IRQ if the vCPU
* is in the guest. If the vCPU is not in the guest, hardware will
* automatically process AVIC interrupts at VMRUN.
*/
if (vcpu->mode == IN_GUEST_MODE) {
/*
* Signal the doorbell to tell hardware to inject the IRQ. If
* the vCPU exits the guest before the doorbell chimes, hardware
* will automatically process AVIC interrupts at the next VMRUN.
*/
avic_ring_doorbell(vcpu);
} else {
/*
* Wake the vCPU if it was blocking. KVM will then detect the
* pending IRQ when checking if the vCPU has a wake event.
*/
kvm_vcpu_wake_up(vcpu);
}
return 0;
}
bool svm_dy_apicv_has_pending_interrupt(struct kvm_vcpu *vcpu)
{
return false;

50
arch/x86/kvm/svm/svm.c
View File

@ -3299,19 +3299,53 @@ static void svm_set_irq(struct kvm_vcpu *vcpu)
SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_INTR;
}
static void svm_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode,
int trig_mode, int vector)
void svm_complete_interrupt_delivery(struct kvm_vcpu *vcpu, int delivery_mode,
int trig_mode, int vector)
{
struct kvm_vcpu *vcpu = apic->vcpu;
/*
* vcpu->arch.apicv_active must be read after vcpu->mode.
* Pairs with smp_store_release in vcpu_enter_guest.
*/
bool in_guest_mode = (smp_load_acquire(&vcpu->mode) == IN_GUEST_MODE);
kvm_lapic_set_irr(vector, apic);
if (svm_deliver_avic_intr(vcpu, vector)) {
if (!READ_ONCE(vcpu->arch.apicv_active)) {
/* Process the interrupt via inject_pending_event */
kvm_make_request(KVM_REQ_EVENT, vcpu);
kvm_vcpu_kick(vcpu);
} else {
trace_kvm_apicv_accept_irq(vcpu->vcpu_id, delivery_mode,
trig_mode, vector);
return;
}
trace_kvm_apicv_accept_irq(vcpu->vcpu_id, delivery_mode, trig_mode, vector);
if (in_guest_mode) {
/*
* Signal the doorbell to tell hardware to inject the IRQ. If
* the vCPU exits the guest before the doorbell chimes, hardware
* will automatically process AVIC interrupts at the next VMRUN.
*/
avic_ring_doorbell(vcpu);
} else {
/*
* Wake the vCPU if it was blocking. KVM will then detect the
* pending IRQ when checking if the vCPU has a wake event.
*/
kvm_vcpu_wake_up(vcpu);
}
}
static void svm_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode,
int trig_mode, int vector)
{
kvm_lapic_set_irr(vector, apic);
/*
* Pairs with the smp_mb_*() after setting vcpu->guest_mode in
* vcpu_enter_guest() to ensure the write to the vIRR is ordered before
* the read of guest_mode. This guarantees that either VMRUN will see
* and process the new vIRR entry, or that svm_complete_interrupt_delivery
* will signal the doorbell if the CPU has already entered the guest.
*/
smp_mb__after_atomic();
svm_complete_interrupt_delivery(apic->vcpu, delivery_mode, trig_mode, vector);
}
static void svm_update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)

4
arch/x86/kvm/svm/svm.h
View File

@ -489,6 +489,8 @@ void svm_set_gif(struct vcpu_svm *svm, bool value);
int svm_invoke_exit_handler(struct kvm_vcpu *vcpu, u64 exit_code);
void set_msr_interception(struct kvm_vcpu *vcpu, u32 *msrpm, u32 msr,
int read, int write);
void svm_complete_interrupt_delivery(struct kvm_vcpu *vcpu, int delivery_mode,
int trig_mode, int vec);
/* nested.c */
@ -572,12 +574,12 @@ bool svm_check_apicv_inhibit_reasons(ulong bit);
void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap);
void svm_hwapic_irr_update(struct kvm_vcpu *vcpu, int max_irr);
void svm_hwapic_isr_update(struct kvm_vcpu *vcpu, int max_isr);
int svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec);
bool svm_dy_apicv_has_pending_interrupt(struct kvm_vcpu *vcpu);
int svm_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
uint32_t guest_irq, bool set);
void avic_vcpu_blocking(struct kvm_vcpu *vcpu);
void avic_vcpu_unblocking(struct kvm_vcpu *vcpu);
void avic_ring_doorbell(struct kvm_vcpu *vcpu);
/* sev.c */

4
arch/x86/kvm/x86.c
View File

@ -9983,7 +9983,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
* result in virtual interrupt delivery.
*/
local_irq_disable();
vcpu->mode = IN_GUEST_MODE;
/* Store vcpu->apicv_active before vcpu->mode. */
smp_store_release(&vcpu->mode, IN_GUEST_MODE);
srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);