Re: [PATCH v2] KVM: x86: Always set kvm_run->if_flag

[Jim Mattson]

On Thu, Dec 9, 2021 at 9:48 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 12/9/21 16:52, Marc Orr wrote:
> > The kvm_run struct's if_flag is a part of the userspace/kernel API. The
> > SEV-ES patches failed to set this flag because it's no longer needed by
> > QEMU (according to the comment in the source code). However, other
> > hypervisors may make use of this flag. Therefore, set the flag for
> > guests with encrypted registers (i.e., with guest_state_protected set).
> >
> > Fixes: f1c6366e3043 ("KVM: SVM: Add required changes to support intercepts under SEV-ES")
> > Signed-off-by: Marc Orr<marcorr@xxxxxxxxxx>
>
> Applied, though I wonder if it is really needed by those other VMMs
> (which? gVisor is the only one that comes to mind that is interested in
> userspace APIC).

Vanadium appears to have one use of it.

> It shouldn't be necessary for in-kernel APIC (where userspace can inject
> interrupts at any time), and ready_for_interrupt_injection is superior
> for userspace APIC.

LOL. Here's that one use...

if (vcpu_run_state_->request_interrupt_window &&
vcpu_run_state_->ready_for_interrupt_injection &&
vcpu_run_state_->if_flag) {
...
}

So, maybe this is much ado about nothing?