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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id a85sm7218993wmd.26.2020.09.02.07.12.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Sep 2020 07:12:57 -0700 (PDT) From: Vitaly Kuznetsov To: Lai Jiangshan , linux-kernel@vger.kernel.org Cc: Lai Jiangshan , Sean Christopherson , Paolo Bonzini , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , kvm@vger.kernel.org Subject: Re: [PATCH V2] kvm x86/mmu: use KVM_REQ_MMU_SYNC to sync when needed In-Reply-To: <20200902135421.31158-1-jiangshanlai@gmail.com> References: <87y2ltx6gl.fsf@vitty.brq.redhat.com> <20200902135421.31158-1-jiangshanlai@gmail.com> Date: Wed, 02 Sep 2020 16:12:55 +0200 Message-ID: <871rjkp8rc.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Lai Jiangshan writes: > From: Lai Jiangshan > > 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) Nit: checkpatch.pl complains here with ERROR: Please use git commit description style 'commit <12+ chars of sha1> ("")' - ie: 'commit 8c8560b83390 ("KVM: x86/mmu: Use KVM_REQ_TLB_FLUSH_CURRENT for MMU specific flushes")' #118: 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); FWIW, Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> but it'd be great to hear from Sean). -- Vitaly