From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752193AbdJ0Ikq (ORCPT ); Fri, 27 Oct 2017 04:40:46 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:52767 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751070AbdJ0Ikn (ORCPT ); Fri, 27 Oct 2017 04:40:43 -0400 X-Google-Smtp-Source: ABhQp+QWPt2VhjLqXrxmFZ4hmTEqaw25lWtdBktgpamVnZNOK+53K6AfMLKHlWCYb0IqIngmLNXj5g== Date: Fri, 27 Oct 2017 10:40:39 +0200 From: Ingo Molnar To: Haozhong Zhang Cc: kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , rkrcmar@redhat.com, Xiao Guangrong , Dan Williams , ivan.d.cuevas.escareno@intel.com, karthik.kumar@intel.com Subject: Re: [PATCH 3/3] KVM: MMU: consider host cache type in MMIO pfn check Message-ID: <20171027084038.j45wuqcw5sb2h3ag@gmail.com> References: <20171027022524.22589-1-haozhong.zhang@intel.com> <20171027022524.22589-4-haozhong.zhang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171027022524.22589-4-haozhong.zhang@intel.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Haozhong Zhang wrote: > By default, KVM treats a reserved page as for MMIO purpose, and maps > it to guest with UC memory type. However, some reserved pages are not > for MMIO, such as pages of DAX device (e.g., /dev/daxX.Y). Mapping > them with UC memory type will harm the performance. In order to > exclude those cases, we check the host cache mode 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 | 32 +++++++++++++++++++++++++++++--- > 1 file changed, 29 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 0b481cc9c725..d4c821a6df3d 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -2707,10 +2707,36 @@ 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)); > + > + /* > + * By default, KVM treats a reserved page as for MMIO > + * purpose, and maps it to guest with UC memory type. > + * However, some reserved pages are not for MMIO, such > + * as pages of DAX device (e.g., /dev/daxX.Y). Mapping > + * them with UC memory type will harm the performance. > + * In order to exclude those cases, we check the host > + * cache mode in addition and only treat UC/UC- pages > + * as MMIO. > + * > + * track_pfn_insert() works only when PAT is enabled, > + * so add pat_enabled() here. > + */ > + if (is_mmio && pat_enabled()) { > + pgprot_t prot; > + enum page_cache_mode cm; > + > + track_pfn_insert(NULL, &prot, kvm_pfn_to_pfn(pfn)); > + cm = pgprot2cachemode(prot); > + is_mmio = (cm == _PAGE_CACHE_MODE_UC || > + cm == _PAGE_CACHE_MODE_UC_MINUS); > + } > + } > + > + return is_mmio; > } > > static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, s/harm the performance /harm performance> But I suspect the rest of the comment should be rewritten too to be more fluid. Beyond that - I think instead of exposing these low level details a properly named helper function should be put into pat.c instead - and KVM can use that. Thanks, Ingo