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([2001:b07:6468:f312:436:e17d:1fd9:d92a]) by smtp.gmail.com with ESMTPSA id c5sm922497wmb.9.2020.01.15.10.20.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Jan 2020 10:20:46 -0800 (PST) Subject: Re: [PATCH] KVM: x86/mmu: Apply max PA check for MMIO sptes to 32-bit KVM To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200108001210.12913-1-sean.j.christopherson@intel.com> From: Paolo Bonzini Message-ID: Date: Wed, 15 Jan 2020 19:20:45 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20200108001210.12913-1-sean.j.christopherson@intel.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/01/20 01:12, Sean Christopherson wrote: > Remove the bogus 64-bit only condition from the check that disables MMIO > spte optimization when the system supports the max PA, i.e. doesn't have > any reserved PA bits. 32-bit KVM always uses PAE paging for the shadow > MMU, and per Intel's SDM: > > PAE paging translates 32-bit linear addresses to 52-bit physical > addresses. > > The kernel's restrictions on max physical addresses are limits on how > much memory the kernel can reasonably use, not what physical addresses > are supported by hardware. > > Fixes: ce88decffd17 ("KVM: MMU: mmio page fault support") > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson > --- > 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 7269130ea5e2..d9c07343d979 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -6191,7 +6191,7 @@ static void kvm_set_mmio_spte_mask(void) > * If reserved bit is not supported, clear the present bit to disable > * mmio page fault. > */ > - if (IS_ENABLED(CONFIG_X86_64) && shadow_phys_bits == 52) > + if (shadow_phys_bits == 52) > mask &= ~1ull; > > kvm_mmu_set_mmio_spte_mask(mask, mask, ACC_WRITE_MASK | ACC_USER_MASK); > Queued, thanks. Paolo