[PATCH 10/21] KVM: nVMX: Unconditionally clear mtf_pending on nested VM-Exit

Sean Christopherson
2022-03-11T03:29:02Z

Clear mtf_pending on nested VM-Exit instead of handling the clear on a
case-by-case basis in vmx_check_nested_events(). The pending MTF should
never survive nested VM-Exit, as it is a property of KVM's run of the
current L2, i.e. should never affect the next L2 run by L1. In practice,
this is likely a nop as getting to L1 with nested_run_pending is
impossible, and KVM doesn't correctly handle morphing a pending exception
that occurs on a prior injected exception (need for re-injected exception
being the other case where MTF isn't cleared). However, KVM will
hopefully soon correctly deal with a pending exception on top of an
injected exception.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/nested.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index b22089ebfe76..82b2d9dde611 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3884,16 +3884,8 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
unsigned long exit_qual;
bool block_nested_events =
vmx->nested.nested_run_pending || kvm_event_needs_reinjection(vcpu);
- bool mtf_pending = vmx->nested.mtf_pending;
struct kvm_lapic *apic = vcpu->arch.apic;

- /*
- * Clear the MTF state. If a higher priority VM-exit is delivered first,
- * this state is discarded.
- */
- if (!block_nested_events)
- vmx->nested.mtf_pending = false;
-
if (lapic_in_kernel(vcpu) &&
test_bit(KVM_APIC_INIT, &apic->pending_events)) {
if (block_nested_events)
@@ -3902,6 +3894,9 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
clear_bit(KVM_APIC_INIT, &apic->pending_events);
if (vcpu->arch.mp_state != KVM_MP_STATE_INIT_RECEIVED)
nested_vmx_vmexit(vcpu, EXIT_REASON_INIT_SIGNAL, 0, 0);
+
+ /* MTF is discarded if the vCPU is in WFS. */
+ vmx->nested.mtf_pending = false;
return 0;
}

@@ -3939,7 +3934,7 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
return 0;
}

- if (mtf_pending) {
+ if (vmx->nested.mtf_pending) {
if (block_nested_events)
return -EBUSY;
nested_vmx_update_pending_dbg(vcpu);
@@ -4532,6 +4527,9 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
struct vcpu_vmx *vmx = to_vmx(vcpu);
struct vmcs12 *vmcs12 = get_vmcs12(vcpu);

+ /* Pending MTF traps are discarded on VM-Exit. */
+ vmx->nested.mtf_pending = false;
+
/* trying to cancel vmlaunch/vmresume is a bug */
WARN_ON_ONCE(vmx->nested.nested_run_pending);

--
2.35.1.723.g4982287a31-goog