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 183EAC433DB for ; Sun, 28 Mar 2021 12:24:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D5510617ED for ; Sun, 28 Mar 2021 12:24:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231126AbhC1MVo (ORCPT ); Sun, 28 Mar 2021 08:21:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:46310 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229503AbhC1MVi (ORCPT ); Sun, 28 Mar 2021 08:21:38 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 80ACF6196C; Sun, 28 Mar 2021 12:21:35 +0000 (UTC) Date: Sun, 28 Mar 2021 13:21:33 +0100 From: Catalin Marinas To: Steven Price Cc: Marc Zyngier , Will Deacon , James Morse , Julien Thierry , Suzuki K Poulose , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave Martin , Mark Rutland , Thomas Gleixner , qemu-devel@nongnu.org, Juan Quintela , "Dr. David Alan Gilbert" , Richard Henderson , Peter Maydell , Haibo Xu , Andrew Jones Subject: Re: [PATCH v10 2/6] arm64: kvm: Introduce MTE VM feature Message-ID: <20210328122131.GB17535@arm.com> References: <20210312151902.17853-1-steven.price@arm.com> <20210312151902.17853-3-steven.price@arm.com> <20210327152324.GA28167@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210327152324.GA28167@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > I now wonder if we can get a MAP_ANONYMOUS mapping of ZONE_DEVICE pfn > even without virtualisation. I haven't checked all the code paths but I don't think we can get a MAP_ANONYMOUS mapping of ZONE_DEVICE memory as we normally need a file descriptor. -- Catalin