Re: [PATCH] KVM: nVMX: Fix IRQs inject to L2 which belong to L1 since race

Jan Kiszka
2014-07-02T09:01:30Z

On 2014-07-02 08:54, Wanpeng Li wrote:
> This patch fix bug https://bugzilla.kernel.org/show_bug.cgi?id=72381
>
> If we didn't inject a still-pending event to L1 since nested_run_pending,
> KVM_REQ_EVENT should be requested after the vmexit in order to inject the
> event to L1. However, current log blindly request a KVM_REQ_EVENT even if
> there is no still-pending event to L1 which blocked by nested_run_pending.
> There is a race which lead to an interrupt will be injected to L2 which
> belong to L1 if L0 send an interrupt to L1 during this window.
>
> VCPU0 another thread
>
> L1 intr not blocked on L2 first entry
> vmx_vcpu_run req event
> kvm check request req event
> check_nested_events don't have any intr
> not nested exit
> intr occur (8254, lapic timer etc)
> inject_pending_event now have intr
> inject interrupt
>
> This patch fix this race by introduced a l1_events_blocked field in nested_vmx
> which indicates there is still-pending event which blocked by nested_run_pending,
> and smart request a KVM_REQ_EVENT if there is a still-pending event which blocked
> by nested_run_pending.

There are more, unrelated reasons why KVM_REQ_EVENT could be set. Why
aren't those able to trigger this scenario?

In any case, unconditionally setting KVM_REQ_EVENT seems strange and
should be changed.

Jan

>
> Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
> ---
> arch/x86/kvm/vmx.c | 20 +++++++++++++++-----
> 1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index f4e5aed..fe69c49 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -372,6 +372,7 @@ struct nested_vmx {
> u64 vmcs01_tsc_offset;
> /* L2 must run next, and mustn't decide to exit to L1. */
> bool nested_run_pending;
> + bool l1_events_blocked;
> /*
> * Guest pages referred to in vmcs02 with host-physical pointers, so
> * we must keep them pinned while L2 runs.
> @@ -7380,8 +7381,10 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
> * we did not inject a still-pending event to L1 now because of
> * nested_run_pending, we need to re-enable this bit.
> */
> - if (vmx->nested.nested_run_pending)
> + if (to_vmx(vcpu)->nested.l1_events_blocked) {
> + to_vmx(vcpu)->nested.l1_events_blocked = false;
> kvm_make_request(KVM_REQ_EVENT, vcpu);
> + }
>
> vmx->nested.nested_run_pending = 0;
>
> @@ -8197,15 +8200,20 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
>
> if (nested_cpu_has_preemption_timer(get_vmcs12(vcpu)) &&
> vmx->nested.preemption_timer_expired) {
> - if (vmx->nested.nested_run_pending)
> + if (vmx->nested.nested_run_pending) {
> + vmx->nested.l1_events_blocked = true;
> return -EBUSY;
> + }
> nested_vmx_vmexit(vcpu, EXIT_REASON_PREEMPTION_TIMER, 0, 0);
> return 0;
> }
>
> if (vcpu->arch.nmi_pending && nested_exit_on_nmi(vcpu)) {
> - if (vmx->nested.nested_run_pending ||
> - vcpu->arch.interrupt.pending)
> + if (vmx->nested.nested_run_pending) {
> + vmx->nested.l1_events_blocked = true;
> + return -EBUSY;
> + }
> + if (vcpu->arch.interrupt.pending)
> return -EBUSY;
> nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI,
> NMI_VECTOR | INTR_TYPE_NMI_INTR |
> @@ -8221,8 +8229,10 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
>
> if ((kvm_cpu_has_interrupt(vcpu) || external_intr) &&
> nested_exit_on_intr(vcpu)) {
> - if (vmx->nested.nested_run_pending)
> + if (vmx->nested.nested_run_pending) {
> + vmx->nested.l1_events_blocked = true;
> return -EBUSY;
> + }
> nested_vmx_vmexit(vcpu, EXIT_REASON_EXTERNAL_INTERRUPT, 0, 0);
> }
>
>

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