Messages in this thread | | | Date | Sat, 28 Jan 2023 00:56:05 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH v2 03/11] KVM: nSVM: explicitly raise KVM_REQ_EVENT on nested VM exit if L1 doesn't intercept interrupts |
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Shortlog is too long, maybe this?
KVM: nSVM: Raise event on nested VM exit if L1 doesn't intercept IRQs
On Tue, Nov 29, 2022, Maxim Levitsky wrote: > If the L2 doesn't intercept interrupts, then the KVM will use vmcb02's
s/the L2/L2, though don't you mean L1?
> V_IRQ for L1 (to detect the interrupt window)
"an interrupt window", i.e. there's not just one window.
> In this case on the nested VM exit KVM might need to copy the V_IRQ bit
s/the nested/nested
> from the vmcb02 to the vmcb01, to continue waiting for the > interrupt window. > > To make it simple, just raise the KVM_REQ_EVENT request, which > execution will lead to the reenabling of the interrupt > window if needed. > > Note that this is a theoretical bug because the KVM already does raise
s/the KVM/KVM
> the KVM_REQ_EVENT request one each nested VM exit because the nested
s/the KVM_REQ_EVENT/KVM_REQ_EVENT, and s/one/on
> VM exit resets RFLAGS and the kvm_set_rflags() raises the > KVM_REQ_EVENT request in the response. > > However raising this request explicitly, together with > documenting why this is needed, is still preferred. > > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com> > --- > arch/x86/kvm/svm/nested.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c > index aad3145b2f62fe..e891318595113e 100644 > --- a/arch/x86/kvm/svm/nested.c > +++ b/arch/x86/kvm/svm/nested.c > @@ -1016,6 +1016,31 @@ int nested_svm_vmexit(struct vcpu_svm *svm) > > svm_switch_vmcb(svm, &svm->vmcb01); > > + /* Note about synchronizing some of int_ctl bits from vmcb02 to vmcb01:
/* * Preferred block comment style...
> + * > + * - V_IRQ, V_IRQ_VECTOR, V_INTR_PRIO_MASK, V_IGN_TPR:
Drop the "-" to be consistent with the rest of the paragraphs.
> + * If the L2 doesn't intercept interrupts, then > + * (even if the L2 does use virtual interrupt masking),
KVM uses "L2" to refer to the thing running at L2. I think what you are referring to here is vmcb12? And that's controlled by L1.
> + * KVM will use the vmcb02's V_INTR to detect interrupt window.
s/the vmcb02/vmcb02
Which of the V_INTR fields does this refer to? Oooh, you're saying the KVM injects a virtual interrupt into L2 using vmcb02 in order to determine when L2 has IRQs enabled.
Why does KVM do that? Why not pend the actual IRQ directly?
> + * > + * In this case, the KVM raises the KVM_REQ_EVENT to ensure that interrupt window
s/the KVM_REQ_EVENT/KVM_REQ_EVENT
> + * is not lost and this implicitly copies these bits from vmcb02 to vmcb01
Too many pronouns. What do "this" and "these bits" refer to?
> + * > + * V_TPR: > + * If the L2 doesn't use virtual interrupt masking, then the L1's vTPR > + * is stored in the vmcb02 but its value doesn't need to be copied from/to > + * vmcb01 because it is copied from/to the TPR APIC's register on > + * each VM entry/exit. > + * > + * V_GIF: > + * - If the nested vGIF is not used, KVM uses vmcb02's V_GIF for L1's V_GIF,
Drop this "-" too.
> + * however, the L1 vGIF is reset to false on each VM exit, thus > + * there is no need to copy it from vmcb02 to vmcb01. > + */ > + > + if (!nested_exit_on_intr(svm)) > + kvm_make_request(KVM_REQ_EVENT, &svm->vcpu); > + > if (unlikely(svm->lbrv_enabled && (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) { > svm_copy_lbrs(vmcb12, vmcb02); > svm_update_lbrv(vcpu); > -- > 2.26.3 >
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