On 2011-02-03 16:02, Avi Kivity wrote:
> The interrupt injection logic looks something like
>
> if an nmi is pending, and nmi injection allowed
> inject nmi
> if an nmi is pending
> request exit on nmi window
>
> the problem is that "nmi is pending" can be set asynchronously by
> the PIT; if it happens to fire between the two if statements, we
> will request an nmi window even though nmi injection is allowed. On
> SVM, this has disasterous results, since it causes eflags.TF to be
> set in random guest code.
Good point. Fortunately never seen on production machines so far here
(we have very moderate NMI rates).
>
> The fix is simple; make nmi_pending asynchronous using the standard
You mean synchronous, no?
> vcpu->requests mechanism; this ensures the code above is completely
> synchronous wrt nmi_pending.
>
> Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 4 +++-
> include/linux/kvm_host.h | 1 +
> 2 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a7f65aa..abe76c0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -360,8 +360,8 @@ void kvm_propagate_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault)
>
> void kvm_inject_nmi(struct kvm_vcpu *vcpu)
> {
> + kvm_make_request(KVM_REQ_NMI, vcpu);
> kvm_make_request(KVM_REQ_EVENT, vcpu);
> - vcpu->arch.nmi_pending = 1;
> }
> EXPORT_SYMBOL_GPL(kvm_inject_nmi);
>
> @@ -5182,6 +5182,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> r = 1;
> goto out;
> }
> + if (kvm_check_request(KVM_REQ_NMI, vcpu))
> + vcpu->arch.nmi_pending = true;
> }
>
> r = kvm_mmu_reload(vcpu);
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index c8dee22..7581090 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -43,6 +43,7 @@
> #define KVM_REQ_DEACTIVATE_FPU 10
> #define KVM_REQ_EVENT 11
> #define KVM_REQ_APF_HALT 12
> +#define KVM_REQ_NMI 13
>
> #define KVM_USERSPACE_IRQ_SOURCE_ID 0
>
Looks good.
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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