linux-kernel - Re: [PATCH v2 2/2] KVM: nSVM: improve SYSENTER emulation on AMD

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Message-ID: <b63e6c63-d781-3aef-a7b8-6b07d3c3568d@redhat.com>
Date:   Thu, 1 Apr 2021 17:57:33 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Sean Christopherson <seanjc@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v2 2/2] KVM: nSVM: improve SYSENTER emulation on AMD

On 01/04/21 17:31, Vitaly Kuznetsov wrote:
>>>> +		svm->sysenter_eip_hi = guest_cpuid_is_intel(vcpu) ? (data >> 32) : 0;
>>> (Personal taste) I'd suggest we keep the whole 'sysenter_eip'/'sysenter_esp'
>>> even if we only use the upper 32 bits of it. That would reduce the code
>>> churn a little bit (no need to change 'struct vcpu_svm').
>> Would there really be less changes?  Consider that you'd have to look at
>> the VMCB anyway because svm_get_msr can be reached not just for guest
>> RDMSR but also for ioctls.
>>
> I was thinking about the hunk in arch/x86/kvm/svm/svm.h tweaking
> vcpu_svm. My opinion is not strong at all here)

Ah okay, if it's just that I would consider the change a benefit, not a 
problem with this patch.

Paolo