From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755546AbdKBJU6 (ORCPT ); Thu, 2 Nov 2017 05:20:58 -0400 Received: from mga03.intel.com ([134.134.136.65]:41477 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755371AbdKBJUx (ORCPT ); Thu, 2 Nov 2017 05:20:53 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,333,1505804400"; d="scan'208";a="170376691" Date: Thu, 2 Nov 2017 17:20:58 +0800 From: Haozhong Zhang To: Xiao Guangrong Cc: kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , rkrcmar@redhat.com, Dan Williams , ivan.d.cuevas.escareno@intel.com, karthik.kumar@intel.com, Ingo Molnar Subject: Re: [PATCH v2 2/2] KVM: MMU: consider host cache mode in MMIO page check Message-ID: <20171102092058.jzh742iimzner3dc@hz-desktop> Mail-Followup-To: Xiao Guangrong , kvm@vger.kernel.org, x86@kernel.org, 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> <824e2162-a6f0-9ca3-e45c-2dbf09a01f1a@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <824e2162-a6f0-9ca3-e45c-2dbf09a01f1a@gmail.com> User-Agent: NeoMutt/20170714 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/02/17 15:56 +0800, Xiao Guangrong wrote: > > > 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. > OK, I'll move the cache mode check to a function in pat.c. Let me wait for Paolo and others' comments. If no additional comments, I'll send another version ASAP. Thanks, Haozhong