From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755183AbdKBH4Q (ORCPT ); Thu, 2 Nov 2017 03:56:16 -0400 Received: from mail-pg0-f65.google.com ([74.125.83.65]:51870 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751587AbdKBH4O (ORCPT ); Thu, 2 Nov 2017 03:56:14 -0400 X-Google-Smtp-Source: ABhQp+QwoPBZlYakic+o7q1L75hjNVFQoW+Tlwg2fRD3x74cVsNY3cjZyJiObAlh9ahpqkD/XdLU6Q== Subject: Re: [PATCH v2 2/2] 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, Dan Williams , ivan.d.cuevas.escareno@intel.com, karthik.kumar@intel.com, Ingo Molnar References: <20171031114840.12615-1-haozhong.zhang@intel.com> <20171031114840.12615-3-haozhong.zhang@intel.com> From: Xiao Guangrong Message-ID: <824e2162-a6f0-9ca3-e45c-2dbf09a01f1a@gmail.com> Date: Thu, 2 Nov 2017 15:56:31 +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: <20171031114840.12615-3-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 10/31/2017 07:48 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 | 30 +++++++++++++++++++++++++++--- > 1 file changed, 27 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 0b481cc9c725..206828d18857 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -2707,10 +2707,34 @@ 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)); > + bool is_mmio = true; > > - return true; > + if (pfn_valid(pfn)) { > + is_mmio = !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 by lookup_memtype() in addition and > + * only treat UC/UC- pages as MMIO. > + * > + * lookup_memtype() works only when PAT is enabled, so > + * add pat_enabled() check here. > + */ > + if (is_mmio && pat_enabled()) { > + enum page_cache_mode cm = lookup_memtype(PFN_PHYS(pfn)); > + > + is_mmio = (cm == _PAGE_CACHE_MODE_UC || > + cm == _PAGE_CACHE_MODE_UC_MINUS); > + } > + } You can move all of these detailed stuffs to pat.c and abstract them by introducing a function, maybe named pat_pfn_is_uc(). I think this is what Ingo wants.