linux-kernel - Re: [PATCH] KVM: x86/mmu: Don't rebuild page when the page is synced and no tlb flushing is required

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Message-Id: <20220325111432.2959162-1-pbonzini@redhat.com>
Date:   Fri, 25 Mar 2022 07:14:34 -0400
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Hou Wenlong <houwenlong.hwl@...group.com>
Cc:     kvm@...r.kernel.org, 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>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/mmu: Don't rebuild page when the page is synced and no tlb flushing is required

> Before Commit c3e5e415bc1e6 ("KVM: X86: Change kvm_sync_page()
> to return true when remote flush is needed"), the return value
> of kvm_sync_page() indicates whether the page is synced, and
> kvm_mmu_get_page() would rebuild page when the sync fails.
> But now, kvm_sync_page() returns false when the page is
> synced and no tlb flushing is required, which leads to
> rebuild page in kvm_mmu_get_page(). So return the return
> value of mmu->sync_page() directly and check it in
> kvm_mmu_get_page(). If the sync fails, the page will be
> zapped and the invalid_list is not empty, so set flush as
> true is accepted in mmu_sync_children().
> 
> Fixes: c3e5e415bc1e6 ("KVM: X86: Change kvm_sync_page() to return true when remote flush is needed")
> Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>

Queued and Cc'ed to stable@, thanks.

Paolo