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.
Add a TODO to document that KVM has an inversion priority bug between
SMIs and MTF (and trap-like #DBS), and that KVM also doesn't properly
save/restore MTF across SMI/RSM.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
arch/x86/kvm/vmx/nested.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 46ea7740bb9e..17df0c31f0b5 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3905,16 +3905,8 @@ 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)
@@ -3923,6 +3915,9 @@ 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;
}
@@ -3945,6 +3940,11 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
* fault-like exceptions, TSS T flag #DB (not emulated by KVM, but
* could theoretically come in from userspace), and ICEBP (INT1).
*
+ * TODO: SMIs have higher priority than MTF and trap-like #DBs (except
+ * for TSS T flag #DBs). KVM also doesn't save/restore pending MTF
+ * across SMI/RSM as it should; that needs to be addressed in order to
+ * prioritize SMI over MTF and trap-like #DBs.
+ *
* Note that only a pending nested run can block a pending exception.
* Otherwise an injected NMI/interrupt should either be
* lost or delivered to the nested hypervisor in the IDT_VECTORING_INFO,
@@ -3960,7 +3960,7 @@ 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);
@@ -4557,6 +4557,9 @@ 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);
--
2.37.1.359.gd136c6c3e2-goog
