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

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Date:   Mon, 6 Dec 2021 20:49:02 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Marc Orr <marcorr@...gle.com>
Cc:     pbonzini@...hat.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,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Always set kvm_run->if_flag

On Mon, Dec 6, 2021 at 8:31 PM Marc Orr <marcorr@...gle.com> wrote:
>
> The kvm_run struct's if_flag is apart of the userspace/kernel API. The

Typo: 'a part'.

> 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 regiesters (i.e., with guest_state_protected set).

Typo: 'registers'.

> Fixes: f1c6366e3043 ("KVM: SVM: Add required changes to support intercepts under SEV-ES")
> Signed-off-by: Marc Orr <marcorr@...gle.com>
> ---

> -       /*
> -        * if_flag is obsolete and useless, so do not bother
> -        * setting it for SEV-ES guests.  Userspace can just
> -        * use kvm_run->ready_for_interrupt_injection.
> -        */
> -       kvm_run->if_flag = !vcpu->arch.guest_state_protected
> -               && (kvm_get_rflags(vcpu) & X86_EFLAGS_IF) != 0;
> -
> +       kvm_run->if_flag = static_call(kvm_x86_get_if_flag)(vcpu);

I'm sorry that I missed that change when it first went by. Maintaining
backwards compatibility with existing userspace code is a fundamental
tenet of Linux kernel development.

Acked-by: Jim Mattson <jmattson@...gle.com>