From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755590AbdKCIv3 (ORCPT ); Fri, 3 Nov 2017 04:51:29 -0400 Received: from mga01.intel.com ([192.55.52.88]:54524 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750805AbdKCIv0 (ORCPT ); Fri, 3 Nov 2017 04:51:26 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,337,1505804400"; d="scan'208";a="1239220284" Date: Fri, 3 Nov 2017 16:51:30 +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, Xiao Guangrong , Dan Williams , ivan.d.cuevas.escareno@intel.com, karthik.kumar@intel.com, Konrad Rzeszutek Wilk , Olif Chapman , Ingo Molnar Subject: Re: [PATCH v4 3/3] KVM: MMU: consider host cache mode in MMIO page check Message-ID: <20171103085130.itjzxoaorvw34vnm@hz-desktop> Mail-Followup-To: Xiao Guangrong , 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, Konrad Rzeszutek Wilk , Olif Chapman , Ingo Molnar References: <20171103055327.21684-1-haozhong.zhang@intel.com> <20171103055327.21684-4-haozhong.zhang@intel.com> <745df599-b65b-bcfe-a20c-05ae6d99a0b5@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <745df599-b65b-bcfe-a20c-05ae6d99a0b5@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 11/03/17 14:54 +0800, Xiao Guangrong wrote: > > > 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? Yes. What I check via pat_enabled() is not only whether PAT support is compiled, but also whether PAT is enabled at runtime. > > It would be better if we move pat_enabled out of kvm as well, Surely I can combine them in one function like bool pat_pfn_is_uc(pfn_t pfn) { enum page_cache_mode cm; if (!pat_enabled()) return false; cm = lookup_memtype(pfn_t_to_phys(pfn)); return cm == _PAGE_CACHE_MODE_UC || cm == _PAGE_CACHE_MODE_UC_MINUS; } but I need a good name to make its semantics clear, or is it enough to just leave a comment like? /* * Check via PAT whether the cache mode of a page if UC or UC-. * * Returns true, if PAT is enabled and the cache mode is UC or UC-. * Returns false otherwise. */ > 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 >