Re: [PATCH v1 2/4] KVM: nSVM: Delay stuffing L2's current RIP into NextRIP until vCPU run

[Yosry Ahmed]

> > We discussed a helper before and you didn't like it, but that was in a
> > different context (a helper that combined normal and special cases).
> > WDYT?
>
> A helper would work.  svm_fixup_nested_rips() is good, the only flaw is the CS.base
> chunk, but I'm not sure I care enough about 32-bit to reject the name just because
> of that :-)
>
> That would make it easier to reduce indentation, e.g.
>
> static void svm_fixup_nested_rips(struct kvm_vcpu *vcpu)
> {
>         struct vcpu_svm *svm = to_svm(vcpu);
>
>         /*
>          * If nrips is supported in hardware but not exposed to L1, stuff the
>          * actual L2 RIP to emulate what a nrips=0 CPU would do (L1 is
>          * responsible for advancing RIP prior to injecting the event). Once L2
>          * runs after L1 executes VMRUN, NextRIP is updated by the CPU and/or
>          * KVM, and this is no longer needed.
>          *
>          * This is done here (as opposed to when preparing vmcb02) to use the
>          * most up-to-date value of RIP regardless of the order of restoring
>          * registers and nested state in the vCPU save+restore path.
>          *
>          * Simiarly, initialize svm->soft_int_* fields here to use the most
>          * up-to-date values of RIP and CS base, regardless of restore order.
>          */
>         if (!is_guest_mode(vcpu) || !svm->nested.nested_run_pending)
>                 return;
>
>         if (boot_cpu_has(X86_FEATURE_NRIPS) &&
>             !guest_cpu_cap_has(vcpu, X86_FEATURE_NRIPS))
>                 svm->vmcb->control.next_rip = kvm_rip_read(vcpu);
>
>         if (svm->soft_int_injected) {
>                 svm->soft_int_csbase = svm->vmcb->save.cs.base;
>                 svm->soft_int_old_rip = kvm_rip_read(vcpu);
>                 if (!guest_cpu_cap_has(vcpu, X86_FEATURE_NRIPS))
>                         svm->soft_int_next_rip = kvm_rip_read(vcpu);
>         }
> }

Looks good, thanks Sean!