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

From: Paolo Bonzini <pbonzini@redhat.com>
To: Hou Wenlong <houwenlong.hwl@antgroup.com>
Cc: kvm@vger.kernel.org, Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
	Lai Jiangshan <laijs@linux.alibaba.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: x86/mmu: Don't rebuild page when the page is synced and no tlb flushing is required
Date: Fri, 25 Mar 2022 07:14:34 -0400	[thread overview]
Message-ID: <20220325111432.2959162-1-pbonzini@redhat.com> (raw)
In-Reply-To: <0dabeeb789f57b0d793f85d073893063e692032d.1647336064.git.houwenlong.hwl@antgroup.com>

> 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@antgroup.com>

Queued and Cc'ed to stable@, thanks.

Paolo