linux-kernel - Re: [PATCH v2] KVM: x86: Always set kvm_run->if

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Date:   Thu, 9 Dec 2021 10:20:22 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Marc Orr <marcorr@...gle.com>, seanjc@...gle.com,
        vkuznets@...hat.com, wanpengli@...cent.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        thomas.lendacky@....com, mlevitsk@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86: Always set kvm_run->if_flag

On Thu, Dec 9, 2021 at 9:48 AM Paolo Bonzini <pbonzini@...hat.com> 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@...gle.com>
>
> 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?