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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, 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 5A8A1C47082 for ; Thu, 3 Jun 2021 16:40:13 +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 17E99613F1 for ; Thu, 3 Jun 2021 16:40:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 17E99613F1 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]:41452 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1loqOC-0002UZ-0S for qemu-devel@archiver.kernel.org; Thu, 03 Jun 2021 12:40:12 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36434) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lopm4-0003JG-Ml for qemu-devel@nongnu.org; Thu, 03 Jun 2021 12:00:48 -0400 Received: from mail.kernel.org ([198.145.29.99]:45004) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1loplv-0007pU-LK for qemu-devel@nongnu.org; Thu, 03 Jun 2021 12:00:48 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0F074613DC; Thu, 3 Jun 2021 16:00:33 +0000 (UTC) Date: Thu, 3 Jun 2021 17:00:31 +0100 From: Catalin Marinas To: Steven Price Subject: Re: [PATCH v13 4/8] KVM: arm64: Introduce MTE VM feature Message-ID: <20210603160031.GE20338@arm.com> References: <20210524104513.13258-1-steven.price@arm.com> <20210524104513.13258-5-steven.price@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210524104513.13258-5-steven.price@arm.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 , "Dr. David Alan Gilbert" , Andrew Jones , Haibo Xu , Suzuki K Poulose , qemu-devel@nongnu.org, Marc Zyngier , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Dave Martin , James Morse , linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu, Julien Thierry Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, May 24, 2021 at 11:45:09AM +0100, Steven Price wrote: > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index c5d1f3c87dbd..226035cf7d6c 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -822,6 +822,42 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot, > return PAGE_SIZE; > } > > +static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn, > + unsigned long size) > +{ > + if (kvm_has_mte(kvm)) { Nitpick (less indentation): if (!kvm_has_mte(kvm)) return 0; > + /* > + * The page will be mapped in stage 2 as Normal Cacheable, so > + * the VM will be able to see the page's tags and therefore > + * they must be initialised first. If PG_mte_tagged is set, > + * tags have already been initialised. > + * pfn_to_online_page() is used to reject ZONE_DEVICE pages > + * that may not support tags. > + */ > + unsigned long i, nr_pages = size >> PAGE_SHIFT; > + struct page *page = pfn_to_online_page(pfn); > + > + if (!page) > + return -EFAULT; > + > + for (i = 0; i < nr_pages; i++, page++) { > + /* > + * There is a potential (but very unlikely) race > + * between two VMs which are sharing a physical page > + * entering this at the same time. However by splitting > + * the test/set the only risk is tags being overwritten > + * by the mte_clear_page_tags() call. > + */ And I think the real risk here is when the page is writable by at least one of the VMs sharing the page. This excludes KSM, so it only leaves the MAP_SHARED mappings. > + if (!test_bit(PG_mte_tagged, &page->flags)) { > + mte_clear_page_tags(page_address(page)); > + set_bit(PG_mte_tagged, &page->flags); > + } > + } If we want to cover this race (I'd say in a separate patch), we can call mte_sync_page_tags(page, __pte(0), false, true) directly (hopefully I got the arguments right). We can avoid the big lock in most cases if kvm_arch_prepare_memory_region() sets a VM_MTE_RESET (tag clear etc.) and __alloc_zeroed_user_highpage() clears the tags on allocation (as we do for VM_MTE but the new flag would not affect the stage 1 VMM page attributes). > + } > + > + return 0; > +} > + > static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > struct kvm_memory_slot *memslot, unsigned long hva, > unsigned long fault_status) > @@ -971,8 +1007,13 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > if (writable) > prot |= KVM_PGTABLE_PROT_W; > > - if (fault_status != FSC_PERM && !device) > + if (fault_status != FSC_PERM && !device) { > + ret = sanitise_mte_tags(kvm, pfn, vma_pagesize); > + if (ret) > + goto out_unlock; Maybe it was discussed in a previous version, why do we need this in addition to kvm_set_spte_gfn()? > + > clean_dcache_guest_page(pfn, vma_pagesize); > + } > > if (exec_fault) { > prot |= KVM_PGTABLE_PROT_X; > @@ -1168,12 +1209,17 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range) > bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range) > { > kvm_pfn_t pfn = pte_pfn(range->pte); > + int ret; > > if (!kvm->arch.mmu.pgt) > return 0; > > WARN_ON(range->end - range->start != 1); > > + ret = sanitise_mte_tags(kvm, pfn, PAGE_SIZE); > + if (ret) > + return false; > + > /* > * We've moved a page around, probably through CoW, so let's treat it > * just like a translation fault and clean the cache to the PoC. Otherwise the patch looks fine. -- Catalin