leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

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

Browse Source 
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@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20220830231614.3580124-12-seanjc@google.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-08-30 23:15:58 +00:00 committed by Paolo Bonzini
parent c2086eca86
commit 593a5c2e3c
1 changed files with 12 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
arch/x86/kvm/vmx/nested.c
View File

@ -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);