linux-kernel - Re: [PATCH] KVM: SVM: Assume a 64-bit hypercall for guests with protected state

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Message-ID: <c6864982-b30a-29b5-9a10-3cfdd331057e@redhat.com>
Date:   Mon, 24 May 2021 16:20:49 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brijesh Singh <brijesh.singh@....com>,
        Ashish Kalra <Ashish.Kalra@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] KVM: SVM: Assume a 64-bit hypercall for guests with
 protected state

On 24/05/21 15:58, Tom Lendacky wrote:
>> Would it hurt if we just move 'vcpu->arch.guest_state_protected' check
>> to is_64_bit_mode() itself? It seems to be too easy to miss this
>> peculiar detail about SEV in review if new is_64_bit_mode() users are to
>> be added.
> I thought about that, but wondered if is_64_bit_mode() was to be used in
> other places in the future, if it would be a concern. I think it would be
> safe since anyone adding it to a new section of code is likely to look at
> what that function is doing first.
> 
> I'm ok with this. Paolo, I know you already queued this, but would you
> prefer moving the check into is_64_bit_mode()?

Let's introduce a new wrapper is_64_bit_hypercall, and add a 
WARN_ON_ONCE(vcpu->arch.guest_state_protected) to is_64_bit_mode.

Paolo