[PATCH v2 22/22] KVM: x86: Replace late check_nested_events() hack with more precise fix

From: Paolo Bonzini
Date: Sat Apr 25 2020 - 03:02:32 EST

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Add an argument to interrupt_allowed and nmi_allowed, to checking if
interrupt injection is blocked. Use the hook to handle the case where
an interrupt arrives between check_nested_events() and the injection
logic. Drop the retry of check_nested_events() that hack-a-fixed the
same condition.

Blocking injection is also a bit of a hack, e.g. KVM should do exiting
and non-exiting interrupt processing in a single pass, but it's a more
precise hack. The old comment is also misleading, e.g. KVM_REQ_EVENT is
purely an optimization, setting it on every run loop (which KVM doesn't
do) should not affect functionality, only performance.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Message-Id: <20200423022550.15113-13-sean.j.christopherson@xxxxxxxxx>
[Extend to SVM, add SMI and NMI. Even though NMI and SMI cannot come
asynchronously right now, making the fix generic is easy and removes a
special case. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 6 +++---
arch/x86/kvm/svm/svm.c | 25 ++++++++++++++++++-----
arch/x86/kvm/vmx/vmx.c | 17 +++++++++++++---
arch/x86/kvm/x86.c | 36 +++++++++++----------------------
4 files changed, 49 insertions(+), 35 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index efaddc68a694..7cd68d1d0627 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1139,8 +1139,8 @@ struct kvm_x86_ops {
void (*set_nmi)(struct kvm_vcpu *vcpu);
void (*queue_exception)(struct kvm_vcpu *vcpu);
void (*cancel_injection)(struct kvm_vcpu *vcpu);
- bool (*interrupt_allowed)(struct kvm_vcpu *vcpu);
- bool (*nmi_allowed)(struct kvm_vcpu *vcpu);
+ bool (*interrupt_allowed)(struct kvm_vcpu *vcpu, bool for_injection);
+ bool (*nmi_allowed)(struct kvm_vcpu *vcpu, bool for_injection);
bool (*get_nmi_mask)(struct kvm_vcpu *vcpu);
void (*set_nmi_mask)(struct kvm_vcpu *vcpu, bool masked);
void (*enable_nmi_window)(struct kvm_vcpu *vcpu);
@@ -1238,7 +1238,7 @@ struct kvm_x86_ops {

void (*setup_mce)(struct kvm_vcpu *vcpu);

- bool (*smi_allowed)(struct kvm_vcpu *vcpu);
+ bool (*smi_allowed)(struct kvm_vcpu *vcpu, bool for_injection);
int (*pre_enter_smm)(struct kvm_vcpu *vcpu, char *smstate);
int (*pre_leave_smm)(struct kvm_vcpu *vcpu, const char *smstate);
int (*enable_smi_window)(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 0bbb2cd24eb7..8f8fc65bfa3e 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3080,13 +3080,17 @@ bool svm_nmi_blocked(struct kvm_vcpu *vcpu)
return ret;
}

-static bool svm_nmi_allowed(struct kvm_vcpu *vcpu)
+static bool svm_nmi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
{
struct vcpu_svm *svm = to_svm(vcpu);
if (svm->nested.nested_run_pending)
return false;

- return !svm_nmi_blocked(vcpu);
+ /* An NMI must not be injected into L2 if it's supposed to VM-Exit. */
+ if (for_injection && is_guest_mode(vcpu) && nested_exit_on_nmi(svm))
+ return false;
+
+ return !svm_nmi_blocked(vcpu);
}

static bool svm_get_nmi_mask(struct kvm_vcpu *vcpu)
@@ -3135,13 +3139,20 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
return (vmcb->control.int_state & SVM_INTERRUPT_SHADOW_MASK);
}

-static bool svm_interrupt_allowed(struct kvm_vcpu *vcpu)
+static bool svm_interrupt_allowed(struct kvm_vcpu *vcpu, bool for_injection)
{
struct vcpu_svm *svm = to_svm(vcpu);
if (svm->nested.nested_run_pending)
return false;

- return !svm_interrupt_blocked(vcpu);
+ /*
+ * An IRQ must not be injected into L2 if it's supposed to VM-Exit,
+ * e.g. if the IRQ arrived asynchronously after checking nested events.
+ */
+ if (for_injection && is_guest_mode(vcpu) && nested_exit_on_intr(svm))
+ return false;
+
+ return !svm_interrupt_blocked(vcpu);
}

static void enable_irq_window(struct kvm_vcpu *vcpu)
@@ -3800,12 +3811,16 @@ bool svm_smi_blocked(struct kvm_vcpu *vcpu)
return is_smm(vcpu);
}

-static bool svm_smi_allowed(struct kvm_vcpu *vcpu)
+static bool svm_smi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
{
struct vcpu_svm *svm = to_svm(vcpu);
if (svm->nested.nested_run_pending)
return false;

+ /* An SMI must not be injected into L2 if it's supposed to VM-Exit. */
+ if (for_injection && is_guest_mode(vcpu) && nested_exit_on_smi(svm))
+ return false;
+
return !svm_smi_blocked(vcpu);
}

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 9e2ba1f96cd1..3ab6ca6062ce 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4524,11 +4524,15 @@ bool vmx_nmi_blocked(struct kvm_vcpu *vcpu)
GUEST_INTR_STATE_NMI));
}

-static bool vmx_nmi_allowed(struct kvm_vcpu *vcpu)
+static bool vmx_nmi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
{
if (to_vmx(vcpu)->nested.nested_run_pending)
return false;

+ /* An NMI must not be injected into L2 if it's supposed to VM-Exit. */
+ if (for_injection && is_guest_mode(vcpu) && nested_exit_on_nmi(vcpu))
+ return false;
+
return !vmx_nmi_blocked(vcpu);
}

@@ -4542,11 +4546,18 @@ bool vmx_interrupt_blocked(struct kvm_vcpu *vcpu)
(GUEST_INTR_STATE_STI | GUEST_INTR_STATE_MOV_SS));
}

-static bool vmx_interrupt_allowed(struct kvm_vcpu *vcpu)
+static bool vmx_interrupt_allowed(struct kvm_vcpu *vcpu, bool for_injection)
{
if (to_vmx(vcpu)->nested.nested_run_pending)
return false;

+ /*
+ * An IRQ must not be injected into L2 if it's supposed to VM-Exit,
+ * e.g. if the IRQ arrived asynchronously after checking nested events.
+ */
+ if (for_injection && is_guest_mode(vcpu) && nested_exit_on_intr(vcpu))
+ return false;
+
return !vmx_interrupt_blocked(vcpu);
}

@@ -7688,7 +7699,7 @@ static void vmx_setup_mce(struct kvm_vcpu *vcpu)
~FEAT_CTL_LMCE_ENABLED;
}

-static bool vmx_smi_allowed(struct kvm_vcpu *vcpu)
+static bool vmx_smi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
{
/* we need a nested vmexit to enter SMM, postpone if run is pending */
if (to_vmx(vcpu)->nested.nested_run_pending)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 44b9d834621c..856b6fc2c2ba 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7746,32 +7746,20 @@ static int inject_pending_event(struct kvm_vcpu *vcpu)
if (kvm_event_needs_reinjection(vcpu))
return 0;

- if (vcpu->arch.smi_pending && kvm_x86_ops.smi_allowed(vcpu)) {
+ if (vcpu->arch.smi_pending &&
+ kvm_x86_ops.smi_allowed(vcpu, true)) {
vcpu->arch.smi_pending = false;
++vcpu->arch.smi_count;
enter_smm(vcpu);
- } else if (vcpu->arch.nmi_pending && kvm_x86_ops.nmi_allowed(vcpu)) {
+ } else if (vcpu->arch.nmi_pending &&
+ kvm_x86_ops.nmi_allowed(vcpu, true)) {
--vcpu->arch.nmi_pending;
vcpu->arch.nmi_injected = true;
kvm_x86_ops.set_nmi(vcpu);
- } else if (kvm_cpu_has_injectable_intr(vcpu)) {
- /*
- * Because interrupts can be injected asynchronously, we are
- * calling check_nested_events again here to avoid a race condition.
- * See https://lkml.org/lkml/2014/7/2/60 for discussion about this
- * proposal and current concerns. Perhaps we should be setting
- * KVM_REQ_EVENT only on certain events and not unconditionally?
- */
- if (is_guest_mode(vcpu)) {
- r = kvm_x86_ops.nested_ops->check_events(vcpu);
- if (r != 0)
- return r;
- }
- if (kvm_x86_ops.interrupt_allowed(vcpu)) {
- kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu),
- false);
- kvm_x86_ops.set_irq(vcpu);
- }
+ } else if (kvm_cpu_has_injectable_intr(vcpu) &&
+ kvm_x86_ops.interrupt_allowed(vcpu, true)) {
+ kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu), false);
+ kvm_x86_ops.set_irq(vcpu);
}

return 0;
@@ -10171,12 +10159,12 @@ static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)

if (kvm_test_request(KVM_REQ_NMI, vcpu) ||
(vcpu->arch.nmi_pending &&
- kvm_x86_ops.nmi_allowed(vcpu)))
+ kvm_x86_ops.nmi_allowed(vcpu, false)))
return true;

if (kvm_test_request(KVM_REQ_SMI, vcpu) ||
(vcpu->arch.smi_pending &&
- kvm_x86_ops.smi_allowed(vcpu)))
+ kvm_x86_ops.smi_allowed(vcpu, false)))
return true;

if (kvm_arch_interrupt_allowed(vcpu) &&
@@ -10228,7 +10216,7 @@ int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)

int kvm_arch_interrupt_allowed(struct kvm_vcpu *vcpu)
{
- return kvm_x86_ops.interrupt_allowed(vcpu);
+ return kvm_x86_ops.interrupt_allowed(vcpu, false);
}

unsigned long kvm_get_linear_rip(struct kvm_vcpu *vcpu)
@@ -10393,7 +10381,7 @@ bool kvm_can_do_async_pf(struct kvm_vcpu *vcpu)
* If interrupts are off we cannot even use an artificial
* halt state.
*/
- return kvm_x86_ops.interrupt_allowed(vcpu);
+ return kvm_arch_interrupt_allowed(vcpu);
}

void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
--
2.18.2

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