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Subject[PATCH 2/3] kvm: x86: do not use KVM_REQ_EVENT for APICv interrupt injection
Date
Since bf9f6ac8d749 ("KVM: Update Posted-Interrupts Descriptor when vCPU
is blocked", 2015-09-18) the posted interrupt descriptor is checked
unconditionally for PIR.ON. Therefore we don't need KVM_REQ_EVENT to
trigger the scan and, if NMIs or SMIs are not involved, we can avoid
the complicated event injection path.

However, there is a race between vmx_deliver_posted_interrupt and
vcpu_enter_guest. Fix it by disabling interrupts before vcpu->mode is
set to IN_GUEST_MODE.

Calling kvm_vcpu_kick if PIR.ON=1 is also useless, though it has been
there since APICv was introduced.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/lapic.c | 2 --
arch/x86/kvm/vmx.c | 8 +++++---
arch/x86/kvm/x86.c | 9 +++++++--
3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 63a442aefc12..be8b7ad56dd1 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -356,8 +356,6 @@ void kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir)
struct kvm_lapic *apic = vcpu->arch.apic;

__kvm_apic_update_irr(pir, apic->regs);
-
- kvm_make_request(KVM_REQ_EVENT, vcpu);
}
EXPORT_SYMBOL_GPL(kvm_apic_update_irr);

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index b33eee395b00..207b9aa32915 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4844,9 +4844,11 @@ static void vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int vector)
if (pi_test_and_set_pir(vector, &vmx->pi_desc))
return;

- r = pi_test_and_set_on(&vmx->pi_desc);
- kvm_make_request(KVM_REQ_EVENT, vcpu);
- if (r || !kvm_vcpu_trigger_posted_interrupt(vcpu))
+ /* If a previous notification has sent the IPI, nothing to do. */
+ if (pi_test_and_set_on(&vmx->pi_desc))
+ return;
+
+ if (!kvm_vcpu_trigger_posted_interrupt(vcpu))
kvm_vcpu_kick(vcpu);
}

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3ee8a91a78c3..604cfbfc5bee 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6658,6 +6658,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
kvm_x86_ops->prepare_guest_switch(vcpu);
if (vcpu->fpu_active)
kvm_load_guest_fpu(vcpu);
+
+ /*
+ * Disable IRQs before setting IN_GUEST_MODE, so that
+ * posted interrupts with vcpu->mode == IN_GUEST_MODE
+ * always result in virtual interrupt delivery.
+ */
+ local_irq_disable();
vcpu->mode = IN_GUEST_MODE;

srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
@@ -6671,8 +6678,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
*/
smp_mb__after_srcu_read_unlock();

- local_irq_disable();
-
if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests
|| need_resched() || signal_pending(current)) {
vcpu->mode = OUTSIDE_GUEST_MODE;
--
1.8.3.1

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