Commit 593a5c2e authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: nVMX: Unconditionally clear mtf_pending on nested VM-Exit 



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: default avatarSean Christopherson <seanjc@google.com>
Reviewed-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20220830231614.3580124-12-seanjc@google.com


Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c2086eca

arch/x86/kvm/vmx/nested.c

+12 −9
Original line number Diff line number Diff line
@@ -3951,16 +3951,8 @@ 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)
@@ -3969,6 +3961,9 @@ 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;

	}
@@ -3991,6 +3986,11 @@ 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,
@@ -4006,7 +4006,7 @@ 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);
@@ -4603,6 +4603,9 @@ 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);