linux-kernel - Re: [RESEND v4 1/2] KVM: VMX: Convert vcpu_vmx.exit

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Date:   Mon, 26 Oct 2020 13:31:06 +0800
From:   Chenyi Qiang <chenyi.qiang@...el.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "Li, Xiaoyao" <xiaoyao.li@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND v4 1/2] KVM: VMX: Convert vcpu_vmx.exit_reason to a union



On 10/21/2020 6:01 AM, Sean Christopherson wrote:
> On Mon, Oct 12, 2020 at 11:35:41AM +0800, Chenyi Qiang wrote:
>> From: Sean Christopherson <sean.j.christopherson@...el.com>
>>
>> Convert vcpu_vmx.exit_reason from a u32 to a union (of size u32).  The
>> full VM_EXIT_REASON field is comprised of a 16-bit basic exit reason in
>> bits 15:0, and single-bit modifiers in bits 31:16.
>>
>> Historically, KVM has only had to worry about handling the "failed
>> VM-Entry" modifier, which could only be set in very specific flows and
>> required dedicated handling.  I.e. manually stripping the FAILED_VMENTRY
>> bit was a somewhat viable approach.  But even with only a single bit to
>> worry about, KVM has had several bugs related to comparing a basic exit
>> reason against the full exit reason store in vcpu_vmx.
>>
>> Upcoming Intel features, e.g. SGX, will add new modifier bits that can
>> be set on more or less any VM-Exit, as opposed to the significantly more
>> restricted FAILED_VMENTRY, i.e. correctly handling everything in one-off
>> flows isn't scalable.  Tracking exit reason in a union forces code to
>> explicitly choose between consuming the full exit reason and the basic
>> exit, and is a convenient way to document and access the modifiers.
>>
>> No functional change intended.
>>
>> Cc: Xiaoyao Li <xiaoyao.li@...el.com>
>> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> This needs your SOB since you are involved in the handling of the patch.
Sorry for the late response, my mailbox encountered some issues...

Will add the SOB here.

>