Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH V2] kvm x86/mmu: use KVM_REQ_MMU_SYNC to sync when needed
To:     Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org
Cc:     Lai Jiangshan <laijs@linux.alibaba.com>,
        Sean Christopherson <sean.j.christopherson@intel.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>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        kvm@vger.kernel.org
References: <87y2ltx6gl.fsf@vitty.brq.redhat.com>
 <20200902135421.31158-1-jiangshanlai@gmail.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <35d079d4-6cb8-b2d0-a4d4-7be92b30a1ea@redhat.com>
Date:   Fri, 11 Sep 2020 19:16:27 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.11.0
MIME-Version: 1.0
In-Reply-To: <20200902135421.31158-1-jiangshanlai@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 02/09/20 15:54, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@linux.alibaba.com>
> 
> When kvm_mmu_get_page() gets a page with unsynced children, the spt
> pagetable is unsynchronized with the guest pagetable. But the
> guest might not issue a "flush" operation on it when the pagetable
> entry is changed from zero or other cases. The hypervisor has the 
> responsibility to synchronize the pagetables.
> 
> The linux kernel behaves as above for many years, But
> 8c8560b83390("KVM: x86/mmu: Use KVM_REQ_TLB_FLUSH_CURRENT for MMU specific flushes)
> inadvertently included a line of code to change it without giving any
> reason in the changelog. It is clear that the commit's intention was to
> change KVM_REQ_TLB_FLUSH -> KVM_REQ_TLB_FLUSH_CURRENT, so we don't
> unneedlesly flush other contexts but one of the hunks changed
> nearby KVM_REQ_MMU_SYNC instead.
> 
> The this patch changes it back.
> 
> Link: https://lore.kernel.org/lkml/20200320212833.3507-26-sean.j.christopherson@intel.com/
> Cc: Sean Christopherson <sean.j.christopherson@intel.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
> ---
> Changed from v1:
> 	update patch description
> 
>  arch/x86/kvm/mmu/mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 4e03841f053d..9a93de921f2b 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2468,7 +2468,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
>  		}
>  
>  		if (sp->unsync_children)
> -			kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
> +			kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);
>  
>  		__clear_sp_write_flooding_count(sp);
>  
> 

Queued, thanks.

Paolo