From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3F8BC43381 for ; Thu, 7 Mar 2019 16:06:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A283C20684 for ; Thu, 7 Mar 2019 16:06:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726351AbfCGQGe (ORCPT ); Thu, 7 Mar 2019 11:06:34 -0500 Received: from mga03.intel.com ([134.134.136.65]:37521 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726186AbfCGQGe (ORCPT ); Thu, 7 Mar 2019 11:06:34 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Mar 2019 08:06:33 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,451,1544515200"; d="scan'208";a="280619539" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.181]) by orsmga004.jf.intel.com with ESMTP; 07 Mar 2019 08:06:33 -0800 Date: Thu, 7 Mar 2019 08:06:33 -0800 From: Sean Christopherson To: Vitaly Kuznetsov Cc: Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , kvm@vger.kernel.org, Junaid Shahid , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 RFC] x86/kvm/mmu: make mmu->prev_roots cache work for NPT case Message-ID: <20190307160633.GA4986@linux.intel.com> References: <0c13c94e-3226-8bfd-2dc7-c75aad1c03a2@redhat.com> <20190223111552.27221-1-vkuznets@redhat.com> <87ftrylqwm.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ftrylqwm.fsf@vitty.brq.redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 07, 2019 at 03:07:05PM +0100, Vitaly Kuznetsov wrote: > Vitaly Kuznetsov writes: > > > Alternative patch: remove the filtering from kvm_mmu_get_page() and check > > for direct on call sites. cr4_pae setting in kvm_calc_mmu_role_common() > > can be preserved for consistency. > > > > Signed-off-by: Vitaly Kuznetsov > > --- > > arch/x86/kvm/mmu.c | 6 ++---- > > 1 file changed, 2 insertions(+), 4 deletions(-) > > > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > > index f2d1d230d5b8..7fb8118f2af6 100644 > > --- a/arch/x86/kvm/mmu.c > > +++ b/arch/x86/kvm/mmu.c > > @@ -2420,8 +2420,6 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, > > role = vcpu->arch.mmu->mmu_role.base; > > role.level = level; > > role.direct = direct; > > - if (role.direct) > > - role.cr4_pae = 0; > > role.access = access; > > if (!vcpu->arch.mmu->direct_map > > && vcpu->arch.mmu->root_level <= PT32_ROOT_LEVEL) { > > @@ -5176,7 +5174,7 @@ static bool detect_write_misaligned(struct kvm_mmu_page *sp, gpa_t gpa, > > gpa, bytes, sp->role.word); > > > > offset = offset_in_page(gpa); > > - pte_size = sp->role.cr4_pae ? 8 : 4; > > + pte_size = (sp->role.cr4_pae && !sp->role.direct) ? 8 : 4; > > > > /* > > * Sometimes, the OS only writes the last one bytes to update status > > @@ -5200,7 +5198,7 @@ static u64 *get_written_sptes(struct kvm_mmu_page *sp, gpa_t gpa, int *nspte) > > page_offset = offset_in_page(gpa); > > level = sp->role.level; > > *nspte = 1; > > - if (!sp->role.cr4_pae) { > > + if (!sp->role.cr4_pae || sp->role.direct) { > > page_offset <<= 1; /* 32->64 */ > > /* > > * A 32-bit pde maps 4MB while the shadow pdes map > > While I personally prefer this approach to not setting role.cr4_pae in > kvm_calc_mmu_role_common() I'd like to get maintainers opinion (I did > test the patch with ept=off but I have to admit I don't know much about > shadow page tables which actually use detect_write_misaligned()/ > get_written_sptes()) > > Paolo, Radim, (anyone else) - any thoughts? The changes to detect_write_misaligned() and get_written_sptes() are wrong/unnecessary as those functions should only be called for indirect shadow PTEs, e.g.: for_each_gfn_indirect_valid_sp(vcpu->kvm, sp, gfn) { if (detect_write_misaligned(sp, gpa, bytes) || detect_write_flooding(sp)) { kvm_mmu_prepare_zap_page(vcpu->kvm, sp, &invalid_list); ++vcpu->kvm->stat.mmu_flooded; continue; } spte = get_written_sptes(sp, gpa, &npte); if (!spte) continue; ... } If anything, they could WARN_ON(sp->role.direct), but IMO that's overkill since they're static helpers with a single call site (above). I'm missing the background for this patch, why does clearing role.cr4_pae for direct SPTEs cause problems with the prev_roots cache?