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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A2734EB64DA for ; Wed, 5 Jul 2023 10:18:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232069AbjGEKSF (ORCPT ); Wed, 5 Jul 2023 06:18:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43492 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231877AbjGEKR4 (ORCPT ); Wed, 5 Jul 2023 06:17:56 -0400 Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9EDD4E3; Wed, 5 Jul 2023 03:17:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1688552275; x=1720088275; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=oLxACQJJ5+O8I5OycraL/46XHwuWjbLPz8/XoWWOHjg=; b=Mnn+HoPz0qna1i0f7IRCiprB16wNIfrQ9e5Z4ahaBsAYwDdtolu1ZHld wL8pm4hFu/OZd7y5XzYyRONPQ+ZkPrLQ+mJ8TNDsmoTccZOk3EumnY5lM Z7Q2SUa6FVHK9rzy8qwbV/1KhzFCTrLaGFwIR/HxjI+A1u/I6X+A2ehJN OjgaKbRGgVcWux9BPz1Lc8R8bTlrIxeUD03E1z4EybMRJaXWgL7kgdwV8 VxUG/Ii6gIfiMFoQKF8Qt8eCtXdjss77/RJyYgwmHDRzy0sRrnvHaWhqW zP3eGdaF6E5EeEHJB6MvaEXr+P8jSWiWsicWh98eWG9zQDhhdWy8iNVh0 w==; X-IronPort-AV: E=McAfee;i="6600,9927,10761"; a="365873180" X-IronPort-AV: E=Sophos;i="6.01,182,1684825200"; d="scan'208";a="365873180" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Jul 2023 03:17:55 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10761"; a="965775138" X-IronPort-AV: E=Sophos;i="6.01,182,1684825200"; d="scan'208";a="965775138" Received: from jialinji-mobl4.ccr.corp.intel.com (HELO localhost) ([10.255.30.200]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Jul 2023 03:17:51 -0700 Date: Wed, 5 Jul 2023 18:18:00 +0800 From: Yu Zhang To: David Stevens Cc: Sean Christopherson , Marc Zyngier , Michael Ellerman , Peter Xu , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org Subject: Re: [PATCH v7 5/8] KVM: x86/mmu: Don't pass FOLL_GET to __kvm_follow_pfn Message-ID: <20230705101800.ut4c6topn6ylwczs@linux.intel.com> References: <20230704075054.3344915-1-stevensd@google.com> <20230704075054.3344915-6-stevensd@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230704075054.3344915-6-stevensd@google.com> User-Agent: NeoMutt/20171215 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 04, 2023 at 04:50:50PM +0900, David Stevens wrote: > From: David Stevens > > Stop passing FOLL_GET to __kvm_follow_pfn. This allows the host to map > memory into the guest that is backed by un-refcounted struct pages - for > example, higher order non-compound pages allocated by the amdgpu driver > via ttm_pool_alloc_page. I guess you mean the tail pages of the higher order non-compound pages? And as to the head page, it is said to be set to one coincidentally[*], and shall not be considered as refcounted. IIUC, refcount of this head page will be increased and decreased soon in hva_to_pfn_remapped(), so this may not be a problem(?). But treating this head page differently, as a refcounted one(e.g., to set the A/D flags), is weired. Or maybe I missed some context, e.g., can the head page be allocted to guest at all? > > The bulk of this change is tracking the is_refcounted_page flag so that > non-refcounted pages don't trigger page_count() == 0 warnings. This is > done by storing the flag in an unused bit in the sptes. Also, maybe we should mention this only works on x86-64. > > Signed-off-by: David Stevens > --- > arch/x86/kvm/mmu/mmu.c | 44 +++++++++++++++++++++------------ > arch/x86/kvm/mmu/mmu_internal.h | 1 + > arch/x86/kvm/mmu/paging_tmpl.h | 9 ++++--- > arch/x86/kvm/mmu/spte.c | 4 ++- > arch/x86/kvm/mmu/spte.h | 12 ++++++++- > arch/x86/kvm/mmu/tdp_mmu.c | 22 ++++++++++------- > 6 files changed, 62 insertions(+), 30 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index e44ab512c3a1..b1607e314497 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c ... > @@ -2937,6 +2943,7 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot, > bool host_writable = !fault || fault->map_writable; > bool prefetch = !fault || fault->prefetch; > bool write_fault = fault && fault->write; > + bool is_refcounted = !fault || fault->is_refcounted_page; Just wonder, what if a non-refcounted page is prefetched? Or is it possible in practice? ... > > @@ -883,7 +884,7 @@ static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, > */ > static int FNAME(sync_spte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, int i) > { > - bool host_writable; > + bool host_writable, is_refcounted; > gpa_t first_pte_gpa; > u64 *sptep, spte; > struct kvm_memory_slot *slot; > @@ -940,10 +941,12 @@ static int FNAME(sync_spte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, int > sptep = &sp->spt[i]; > spte = *sptep; > host_writable = spte & shadow_host_writable_mask; > + // TODO: is this correct? > + is_refcounted = spte & SPTE_MMU_PAGE_REFCOUNTED; > slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn); > make_spte(vcpu, sp, slot, pte_access, gfn, > spte_to_pfn(spte), spte, true, false, > - host_writable, &spte); > + host_writable, is_refcounted, &spte); Could we restrict that a non-refcounted page shall not be used as shadow page? [*] https://lore.kernel.org/all/8caf3008-dcf3-985a-631e-e019b277c6f0@amd.com/ B.R. Yu