From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754584AbdKCGx5 (ORCPT ); Fri, 3 Nov 2017 02:53:57 -0400 Received: from mail-io0-f194.google.com ([209.85.223.194]:46875 "EHLO mail-io0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750805AbdKCGxy (ORCPT ); Fri, 3 Nov 2017 02:53:54 -0400 X-Google-Smtp-Source: ABhQp+Rcolfb+snqN5jcWAtFMMMakpwIyta7GKAk+HbtHTzL+YMYtUjYmLV/1GdrdlpXMamnTr5kKQ== Subject: Re: [PATCH v4 3/3] KVM: MMU: consider host cache mode in MMIO page check To: Haozhong Zhang , kvm@vger.kernel.org, x86@kernel.org Cc: linux-kernel@vger.kernel.org, Paolo Bonzini , rkrcmar@redhat.com, Xiao Guangrong , Dan Williams , ivan.d.cuevas.escareno@intel.com, karthik.kumar@intel.com, Konrad Rzeszutek Wilk , Olif Chapman , Ingo Molnar References: <20171103055327.21684-1-haozhong.zhang@intel.com> <20171103055327.21684-4-haozhong.zhang@intel.com> From: Xiao Guangrong Message-ID: <745df599-b65b-bcfe-a20c-05ae6d99a0b5@gmail.com> Date: Fri, 3 Nov 2017 14:54:13 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20171103055327.21684-4-haozhong.zhang@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/03/2017 01:53 PM, Haozhong Zhang wrote: > Some reserved pages, such as those from NVDIMM DAX devices, are > not for MMIO, and can be mapped with cached memory type for better > performance. However, the above check misconceives those pages as > MMIO. Because KVM maps MMIO pages with UC memory type, the > performance of guest accesses to those pages would be harmed. > Therefore, we check the host memory type by lookup_memtype() in > addition and only treat UC/UC- pages as MMIO. > > Signed-off-by: Haozhong Zhang > Reported-by: Cuevas Escareno, Ivan D > Reported-by: Kumar, Karthik > --- > arch/x86/kvm/mmu.c | 19 ++++++++++++++++++- > 1 file changed, 18 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 0b481cc9c725..e9ed0e666a83 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -2708,7 +2708,24 @@ static bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn, > static bool kvm_is_mmio_pfn(kvm_pfn_t pfn) > { > if (pfn_valid(pfn)) > - return !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn)); > + return !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn)) && > + /* > + * Some reserved pages, such as those from > + * NVDIMM DAX devices, are not for MMIO, and > + * can be mapped with cached memory type for > + * better performance. However, the above > + * check misconceives those pages as MMIO. > + * Because KVM maps MMIO pages with UC memory > + * type, the performance of guest accesses to > + * those pages would be harmed. Therefore, we > + * check the host memory type in addition and > + * only treat UC/UC- pages as MMIO. > + * > + * pat_pfn_is_uc() works only when PAT is enabled, > + * so check pat_enabled() as well. > + */ > + (!pat_enabled() || > + pat_pfn_is_uc(kvm_pfn_t_to_pfn_t(pfn))); Can it be compiled if !CONFIG_PAT? It would be better if we move pat_enabled out of kvm as well, please refer to pgprot_writecombine() which is implemented in pat.c and in include\asm-generic\pgtable.h: #ifndef pgprot_writecombine #define pgprot_writecombine pgprot_noncached #endif