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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 DCC1DC433C1 for ; Wed, 31 Mar 2021 09:22:21 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 952A96198F for ; Wed, 31 Mar 2021 09:22:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 952A96198F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:35404 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lRX3M-000804-PY for qemu-devel@archiver.kernel.org; Wed, 31 Mar 2021 05:22:20 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44454) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lRX2S-00078u-TZ for qemu-devel@nongnu.org; Wed, 31 Mar 2021 05:21:26 -0400 Received: from mail.kernel.org ([198.145.29.99]:56224) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lRX2M-00086k-Qe for qemu-devel@nongnu.org; Wed, 31 Mar 2021 05:21:23 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9835B617C9; Wed, 31 Mar 2021 09:21:12 +0000 (UTC) Date: Wed, 31 Mar 2021 10:21:10 +0100 From: Catalin Marinas To: David Hildenbrand Subject: Re: [PATCH v10 2/6] arm64: kvm: Introduce MTE VM feature Message-ID: <20210331092109.GA21921@arm.com> References: <20210312151902.17853-1-steven.price@arm.com> <20210312151902.17853-3-steven.price@arm.com> <20210327152324.GA28167@arm.com> <20210328122131.GB17535@arm.com> <20210330103013.GD18075@arm.com> <8977120b-841d-4882-2472-6e403bc9c797@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8977120b-841d-4882-2472-6e403bc9c797@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Received-SPF: pass client-ip=198.145.29.99; envelope-from=cmarinas@kernel.org; helo=mail.kernel.org X-Spam_score_int: -66 X-Spam_score: -6.7 X-Spam_bar: ------ X-Spam_report: (-6.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Peter Maydell , Andrew Jones , Haibo Xu , Suzuki K Poulose , qemu-devel@nongnu.org, Marc Zyngier , Juan Quintela , Richard Henderson , "Dr. David Alan Gilbert" , Steven Price , James Morse , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, Thomas Gleixner , Julien Thierry , Will Deacon , Dave Martin , linux-kernel@vger.kernel.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Mar 31, 2021 at 09:34:44AM +0200, David Hildenbrand wrote: > On 30.03.21 12:30, Catalin Marinas wrote: > > On Mon, Mar 29, 2021 at 05:06:51PM +0100, Steven Price wrote: > > > On 28/03/2021 13:21, Catalin Marinas wrote: > > > > On Sat, Mar 27, 2021 at 03:23:24PM +0000, Catalin Marinas wrote: > > > > > On Fri, Mar 12, 2021 at 03:18:58PM +0000, Steven Price wrote: > > > > > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > > > > > > index 77cb2d28f2a4..b31b7a821f90 100644 > > > > > > --- a/arch/arm64/kvm/mmu.c > > > > > > +++ b/arch/arm64/kvm/mmu.c > > > > > > @@ -879,6 +879,22 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > > > > > > if (vma_pagesize == PAGE_SIZE && !force_pte) > > > > > > vma_pagesize = transparent_hugepage_adjust(memslot, hva, > > > > > > &pfn, &fault_ipa); > > > > > > + > > > > > > + if (fault_status != FSC_PERM && kvm_has_mte(kvm) && pfn_valid(pfn)) { > > > > > > + /* > > > > > > + * VM will be able to see the page's tags, so we must ensure > > > > > > + * they have been initialised. if PG_mte_tagged is set, tags > > > > > > + * have already been initialised. > > > > > > + */ > > > > > > + struct page *page = pfn_to_page(pfn); > > > > > > + unsigned long i, nr_pages = vma_pagesize >> PAGE_SHIFT; > > > > > > + > > > > > > + for (i = 0; i < nr_pages; i++, page++) { > > > > > > + if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > > > > > > + mte_clear_page_tags(page_address(page)); > > > > > > + } > > > > > > + } > > > > > > > > > > This pfn_valid() check may be problematic. Following commit eeb0753ba27b > > > > > ("arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory"), it returns > > > > > true for ZONE_DEVICE memory but such memory is allowed not to support > > > > > MTE. > > > > > > > > Some more thinking, this should be safe as any ZONE_DEVICE would be > > > > mapped as untagged memory in the kernel linear map. It could be slightly > > > > inefficient if it unnecessarily tries to clear tags in ZONE_DEVICE, > > > > untagged memory. Another overhead is pfn_valid() which will likely end > > > > up calling memblock_is_map_memory(). > > > > > > > > However, the bigger issue is that Stage 2 cannot disable tagging for > > > > Stage 1 unless the memory is Non-cacheable or Device at S2. Is there a > > > > way to detect what gets mapped in the guest as Normal Cacheable memory > > > > and make sure it's only early memory or hotplug but no ZONE_DEVICE (or > > > > something else like on-chip memory)? If we can't guarantee that all > > > > Cacheable memory given to a guest supports tags, we should disable the > > > > feature altogether. > > > > > > In stage 2 I believe we only have two types of mapping - 'normal' or > > > DEVICE_nGnRE (see stage2_map_set_prot_attr()). Filtering out the latter is a > > > case of checking the 'device' variable, and makes sense to avoid the > > > overhead you describe. > > > > > > This should also guarantee that all stage-2 cacheable memory supports tags, > > > as kvm_is_device_pfn() is simply !pfn_valid(), and pfn_valid() should only > > > be true for memory that Linux considers "normal". > > If you think "normal" == "normal System RAM", that's wrong; see below. By "normal" I think both Steven and I meant the Normal Cacheable memory attribute (another being the Device memory attribute). > > That's the problem. With Anshuman's commit I mentioned above, > > pfn_valid() returns true for ZONE_DEVICE mappings (e.g. persistent > > memory, not talking about some I/O mapping that requires Device_nGnRE). > > So kvm_is_device_pfn() is false for such memory and it may be mapped as > > Normal but it is not guaranteed to support tagging. > > pfn_valid() means "there is a struct page"; if you do pfn_to_page() and > touch the page, you won't fault. So Anshuman's commit is correct. I agree. > pfn_to_online_page() means, "there is a struct page and it's system RAM > that's in use; the memmap has a sane content" Does pfn_to_online_page() returns a valid struct page pointer for ZONE_DEVICE pages? IIUC, these are not guaranteed to be system RAM, for some definition of system RAM (I assume NVDIMM != system RAM). For example, pmem_attach_disk() calls devm_memremap_pages() and this would use the Normal Cacheable memory attribute without necessarily being system RAM. So if pfn_valid() is not equivalent to system RAM, we have a potential issue with MTE. Even if "system RAM" includes NVDIMMs, we still have this issue and we may need a new term to describe MTE-safe memory. In the kernel we assume MTE-safe all pages that can be mapped as MAP_ANONYMOUS and I don't think these include ZONE_DEVICE pages. Thanks. -- Catalin