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Subject[PATCH 02/28] KVM: x86: enable event window in inject_pending_event
Date
In case an interrupt arrives after nested.check_events but before the
call to kvm_cpu_has_injectable_intr, we could end up enabling the interrupt
window even if the interrupt is actually going to be a vmexit. This is
useless rather than harmful, but it really complicates reasoning about
SVM's handling of the VINTR intercept. We'd like to never bother with
the VINTR intercept if V_INTR_MASKING=1 && INTERCEPT_INTR=1, because in
that case there is no interrupt window and we can just exit the nested
guest whenever we want.

As a first step, this patch moves the opening of the interrupt
window inside inject_pending_event. This consolidates the check for
pending interrupt/NMI/SMI in one place, removing the repeated call to
kvm_cpu_has_injectable_intr.

The main functional change here is that re-injection of still-pending
events will also use req_immediate_exit instead of using interrupt-window
intercepts.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 8 +--
arch/x86/kvm/svm/svm.c | 24 +++----
arch/x86/kvm/vmx/vmx.c | 20 +++---
arch/x86/kvm/x86.c | 112 +++++++++++++++++---------------
4 files changed, 87 insertions(+), 77 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index db261da578f3..7707bd4b0593 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1136,8 +1136,8 @@ 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 for_injection);
- bool (*nmi_allowed)(struct kvm_vcpu *vcpu, bool for_injection);
+ int (*interrupt_allowed)(struct kvm_vcpu *vcpu, bool for_injection);
+ int (*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);
@@ -1234,10 +1234,10 @@ struct kvm_x86_ops {

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

- bool (*smi_allowed)(struct kvm_vcpu *vcpu, bool for_injection);
+ int (*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);
+ void (*enable_smi_window)(struct kvm_vcpu *vcpu);

int (*mem_enc_op)(struct kvm *kvm, void __user *argp);
int (*mem_enc_reg_region)(struct kvm *kvm, struct kvm_enc_region *argp);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 9987f6fe9d88..9ac9963405b5 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3053,15 +3053,15 @@ bool svm_nmi_blocked(struct kvm_vcpu *vcpu)
return ret;
}

-static bool svm_nmi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
+static int 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 -EBUSY;

/* 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 -EBUSY;

return !svm_nmi_blocked(vcpu);
}
@@ -3112,18 +3112,18 @@ 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, bool for_injection)
+static int 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 -EBUSY;

/*
* 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 -EBUSY;

return !svm_interrupt_blocked(vcpu);
}
@@ -3793,15 +3793,15 @@ bool svm_smi_blocked(struct kvm_vcpu *vcpu)
return is_smm(vcpu);
}

-static bool svm_smi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
+static int 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;
+ return -EBUSY;

/* 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 -EBUSY;

return !svm_smi_blocked(vcpu);
}
@@ -3848,7 +3848,7 @@ static int svm_pre_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
return 0;
}

-static int enable_smi_window(struct kvm_vcpu *vcpu)
+static void enable_smi_window(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);

@@ -3856,9 +3856,9 @@ static int enable_smi_window(struct kvm_vcpu *vcpu)
if (vgif_enabled(svm))
set_intercept(svm, INTERCEPT_STGI);
/* STGI will cause a vm exit */
- return 1;
+ } else {
+ /* We must be in SMM; RSM will cause a vmexit anyway. */
}
- return 0;
}

static bool svm_need_emulation_on_page_fault(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 55712dd86baf..aedc46407b1f 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4552,14 +4552,14 @@ bool vmx_nmi_blocked(struct kvm_vcpu *vcpu)
GUEST_INTR_STATE_NMI));
}

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

/* 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 -EBUSY;

return !vmx_nmi_blocked(vcpu);
}
@@ -4574,17 +4574,17 @@ 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, bool for_injection)
+static int vmx_interrupt_allowed(struct kvm_vcpu *vcpu, bool for_injection)
{
if (to_vmx(vcpu)->nested.nested_run_pending)
- return false;
+ return -EBUSY;

/*
* 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 -EBUSY;

return !vmx_interrupt_blocked(vcpu);
}
@@ -7755,11 +7755,11 @@ static void vmx_setup_mce(struct kvm_vcpu *vcpu)
~FEAT_CTL_LMCE_ENABLED;
}

-static bool vmx_smi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
+static int 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)
- return false;
+ return -EBUSY;
return !is_smm(vcpu);
}

@@ -7797,9 +7797,9 @@ static int vmx_pre_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
return 0;
}

-static int enable_smi_window(struct kvm_vcpu *vcpu)
+static void enable_smi_window(struct kvm_vcpu *vcpu)
{
- return 0;
+ /* RSM will cause a vmexit anyway. */
}

static bool vmx_need_emulation_on_page_fault(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 064a7ea0e671..192238841cac 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7710,7 +7710,7 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu)
kvm_x86_ops.update_cr8_intercept(vcpu, tpr, max_irr);
}

-static int inject_pending_event(struct kvm_vcpu *vcpu)
+static void inject_pending_event(struct kvm_vcpu *vcpu, bool *req_immediate_exit)
{
int r;
bool can_inject = true;
@@ -7756,8 +7756,8 @@ static int inject_pending_event(struct kvm_vcpu *vcpu)
*/
if (is_guest_mode(vcpu)) {
r = kvm_x86_ops.nested_ops->check_events(vcpu);
- if (r != 0)
- return r;
+ if (r < 0)
+ goto busy;
}

/* try to inject new event if pending */
@@ -7795,27 +7795,64 @@ static int inject_pending_event(struct kvm_vcpu *vcpu)
can_inject = false;
}

- /* Finish re-injection before considering new events */
- if (!can_inject)
- return 0;
+ /*
+ * Finally, either inject the event or enable window-open exits.
+ * If an event is pending but cannot be injected right now (for
+ * example if it just arrived and we have to inject it as a
+ * vmexit), then we request an immediate exit. This is indicated
+ * by a -EBUSY return value from kvm_x86_ops.*_allowed.
+ */
+ if (vcpu->arch.smi_pending) {
+ r = can_inject ? kvm_x86_ops.smi_allowed(vcpu, true) : -EBUSY;
+ if (r < 0)
+ goto busy;
+ if (r) {
+ vcpu->arch.smi_pending = false;
+ ++vcpu->arch.smi_count;
+ enter_smm(vcpu);
+ can_inject = false;
+ } else {
+ kvm_x86_ops.enable_smi_window(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, true)) {
- --vcpu->arch.nmi_pending;
- vcpu->arch.nmi_injected = true;
- kvm_x86_ops.set_nmi(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);
+ if (vcpu->arch.nmi_pending) {
+ r = can_inject ? kvm_x86_ops.nmi_allowed(vcpu, true) : -EBUSY;
+ if (r < 0)
+ goto busy;
+ if (r) {
+ --vcpu->arch.nmi_pending;
+ vcpu->arch.nmi_injected = true;
+ kvm_x86_ops.set_nmi(vcpu);
+ can_inject = false;
+ } else {
+ kvm_x86_ops.enable_nmi_window(vcpu);
+ }
}

- return 0;
+ if (kvm_cpu_has_injectable_intr(vcpu)) {
+ r = can_inject ? kvm_x86_ops.interrupt_allowed(vcpu, true) : -EBUSY;
+ if (r < 0)
+ goto busy;
+ if (r) {
+ kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu), false);
+ kvm_x86_ops.set_irq(vcpu);
+ } else {
+ kvm_x86_ops.enable_irq_window(vcpu);
+ }
+ }
+
+ if (is_guest_mode(vcpu) &&
+ kvm_x86_ops.nested_ops->hv_timer_pending &&
+ kvm_x86_ops.nested_ops->hv_timer_pending(vcpu))
+ *req_immediate_exit = true;
+
+ WARN_ON(vcpu->arch.exception.pending);
+ return;
+
+busy:
+ *req_immediate_exit = true;
+ return;
}

static void process_nmi(struct kvm_vcpu *vcpu)
@@ -8353,36 +8390,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
goto out;
}

- if (inject_pending_event(vcpu) != 0)
- req_immediate_exit = true;
- else {
- /* Enable SMI/NMI/IRQ window open exits if needed.
- *
- * SMIs have three cases:
- * 1) They can be nested, and then there is nothing to
- * do here because RSM will cause a vmexit anyway.
- * 2) There is an ISA-specific reason why SMI cannot be
- * injected, and the moment when this changes can be
- * intercepted.
- * 3) Or the SMI can be pending because
- * inject_pending_event has completed the injection
- * of an IRQ or NMI from the previous vmexit, and
- * then we request an immediate exit to inject the
- * SMI.
- */
- if (vcpu->arch.smi_pending && !is_smm(vcpu))
- if (!kvm_x86_ops.enable_smi_window(vcpu))
- req_immediate_exit = true;
- if (vcpu->arch.nmi_pending)
- kvm_x86_ops.enable_nmi_window(vcpu);
- if (kvm_cpu_has_injectable_intr(vcpu) || req_int_win)
- kvm_x86_ops.enable_irq_window(vcpu);
- if (is_guest_mode(vcpu) &&
- kvm_x86_ops.nested_ops->hv_timer_pending &&
- kvm_x86_ops.nested_ops->hv_timer_pending(vcpu))
- req_immediate_exit = true;
- WARN_ON(vcpu->arch.exception.pending);
- }
+ inject_pending_event(vcpu, &req_immediate_exit);
+ if (req_int_win)
+ kvm_x86_ops.enable_irq_window(vcpu);

if (kvm_lapic_enabled(vcpu)) {
update_cr8_intercept(vcpu);
--
2.26.2

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