linux-kernel - Re: [PATCH 2/4] KVM: X86: Cache CR3 in prev

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Message-ID: <CAJhGHyA-L9HTidmPt4nz=KbYySuEU1hkBdZPaznwUPp008HBFg@mail.gmail.com>
Date:   Fri, 22 Oct 2021 10:11:01 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 2/4] KVM: X86: Cache CR3 in prev_roots when PCID is disabled

On Fri, Oct 22, 2021 at 1:43 AM Paolo Bonzini <pbonzini@...hat.com> wrote:

>
>           * If CR4.PCIDE is changed 1 -> 0, the guest TLB must be flushed.
>           * If CR4.PCIDE is changed 0 -> 1, there is no need to flush the TLB
>           * according to the SDM; however, stale prev_roots could be reused
>           * reused incorrectly by MOV to CR3 with NOFLUSH=1, so we free them
>           * all.  KVM_REQ_MMU_RELOAD is fit for the both cases; it
>           * is slow, but changing CR4.PCIDE is a rare case.
>

There is a double "reused" separated by "\".

>
>
> Can you confirm the above comments are accurate?
>

Yes, they are better and consistent with what I meant, only one redundant
"reused" in the comments.

thanks
Lai