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=-12.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,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 A5ECDC433C1 for ; Wed, 31 Mar 2021 07:35:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6BA17619D3 for ; Wed, 31 Mar 2021 07:35:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234091AbhCaHfA (ORCPT ); Wed, 31 Mar 2021 03:35:00 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:34084 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234063AbhCaHe4 (ORCPT ); Wed, 31 Mar 2021 03:34:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1617176095; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Rw79CBvMLi5mEY0tcvp9kTn6CghMbW3t144/yxRDUX4=; b=HvURMu1hUDFg7UEMiYVY4j7YvBeOgTeyQEAZ7Q1eG9jmWhni9ntk9RV4nzdd988o4QXnSr ezxT42ztPe4w11EqctwdLowVCBvliDNyoRdiFSdqLOg0EEos8qvkqFQGZUyFghuy/2Ctj7 MujZpK9uFLuHNNZrAE712v83HG/N3Ns= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-260-Q4AVGFAoNCuvO8_eHBIvbQ-1; Wed, 31 Mar 2021 03:34:52 -0400 X-MC-Unique: Q4AVGFAoNCuvO8_eHBIvbQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 87C43108BD09; Wed, 31 Mar 2021 07:34:50 +0000 (UTC) Received: from [10.36.113.60] (ovpn-113-60.ams2.redhat.com [10.36.113.60]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5582D5C5AE; Wed, 31 Mar 2021 07:34:45 +0000 (UTC) To: Catalin Marinas , Steven Price 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 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> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH v10 2/6] arm64: kvm: Introduce MTE VM feature Message-ID: <8977120b-841d-4882-2472-6e403bc9c797@redhat.com> Date: Wed, 31 Mar 2021 09:34:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210330103013.GD18075@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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. 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" > > For user MTE, we get away with this as the MAP_ANONYMOUS requirement > would filter it out while arch_add_memory() will ensure it's mapped as > untagged in the linear map. See another recent fix for hotplugged > memory: d15dfd31384b ("arm64: mte: Map hotplugged memory as Normal > Tagged"). We needed to ensure that ZONE_DEVICE doesn't end up as tagged, > only hoplugged memory. Both handled via arch_add_memory() in the arch > code with ZONE_DEVICE starting at devm_memremap_pages(). > >>>> 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. >> >> I certainly hope this is the case - it's the weird corner cases of device >> drivers that worry me. E.g. I know i915 has a "hidden" mmap behind an ioctl >> (see i915_gem_mmap_ioctl(), although this case is fine - it's MAP_SHARED). >> Mali's kbase did something similar in the past. > > I think this should be fine since it's not a MAP_ANONYMOUS (we do allow > MAP_SHARED to be tagged). > -- Thanks, David / dhildenb 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=-10.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,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 8A988C433C1 for ; Wed, 31 Mar 2021 07:36:05 +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 1A0546192C for ; 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Wed, 31 Mar 2021 07:34:50 +0000 (UTC) Received: from [10.36.113.60] (ovpn-113-60.ams2.redhat.com [10.36.113.60]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5582D5C5AE; Wed, 31 Mar 2021 07:34:45 +0000 (UTC) To: Catalin Marinas , Steven Price 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> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH v10 2/6] arm64: kvm: Introduce MTE VM feature Message-ID: <8977120b-841d-4882-2472-6e403bc9c797@redhat.com> Date: Wed, 31 Mar 2021 09:34:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210330103013.GD18075@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, 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 , Marc Zyngier , Juan Quintela , Richard Henderson , "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, 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 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. > > 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. 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" > > For user MTE, we get away with this as the MAP_ANONYMOUS requirement > would filter it out while arch_add_memory() will ensure it's mapped as > untagged in the linear map. See another recent fix for hotplugged > memory: d15dfd31384b ("arm64: mte: Map hotplugged memory as Normal > Tagged"). We needed to ensure that ZONE_DEVICE doesn't end up as tagged, > only hoplugged memory. Both handled via arch_add_memory() in the arch > code with ZONE_DEVICE starting at devm_memremap_pages(). > >>>> 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. >> >> I certainly hope this is the case - it's the weird corner cases of device >> drivers that worry me. E.g. I know i915 has a "hidden" mmap behind an ioctl >> (see i915_gem_mmap_ioctl(), although this case is fine - it's MAP_SHARED). >> Mali's kbase did something similar in the past. > > I think this should be fine since it's not a MAP_ANONYMOUS (we do allow > MAP_SHARED to be tagged). > -- Thanks, David / dhildenb 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=-10.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 1334FC433E1 for ; Wed, 31 Mar 2021 07:35:00 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 74560619DB for ; 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Wed, 31 Mar 2021 03:34:52 -0400 X-MC-Unique: Q4AVGFAoNCuvO8_eHBIvbQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 87C43108BD09; Wed, 31 Mar 2021 07:34:50 +0000 (UTC) Received: from [10.36.113.60] (ovpn-113-60.ams2.redhat.com [10.36.113.60]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5582D5C5AE; Wed, 31 Mar 2021 07:34:45 +0000 (UTC) To: Catalin Marinas , Steven Price 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> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH v10 2/6] arm64: kvm: Introduce MTE VM feature Message-ID: <8977120b-841d-4882-2472-6e403bc9c797@redhat.com> Date: Wed, 31 Mar 2021 09:34:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210330103013.GD18075@arm.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Cc: Marc Zyngier , Juan Quintela , Richard Henderson , "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, Thomas Gleixner , Will Deacon , Dave Martin , linux-kernel@vger.kernel.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu 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. > > 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. 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" > > For user MTE, we get away with this as the MAP_ANONYMOUS requirement > would filter it out while arch_add_memory() will ensure it's mapped as > untagged in the linear map. See another recent fix for hotplugged > memory: d15dfd31384b ("arm64: mte: Map hotplugged memory as Normal > Tagged"). We needed to ensure that ZONE_DEVICE doesn't end up as tagged, > only hoplugged memory. Both handled via arch_add_memory() in the arch > code with ZONE_DEVICE starting at devm_memremap_pages(). > >>>> 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. >> >> I certainly hope this is the case - it's the weird corner cases of device >> drivers that worry me. E.g. I know i915 has a "hidden" mmap behind an ioctl >> (see i915_gem_mmap_ioctl(), although this case is fine - it's MAP_SHARED). >> Mali's kbase did something similar in the past. > > I think this should be fine since it's not a MAP_ANONYMOUS (we do allow > MAP_SHARED to be tagged). > -- Thanks, David / dhildenb _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 14660C433C1 for ; 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bh=Rw79CBvMLi5mEY0tcvp9kTn6CghMbW3t144/yxRDUX4=; b=BeQwDtesem7/mZ6xSKmEooYioSzYt8lEsbTRw+ZyiZaE8LJc1/do69sO4buqoFNLlOU+cl +1S/cGha+NtmgRrSZP7jyyfEzBhkW8Xjl003dqdImulJT6saO/iuBYrM8Zbln79dtihSHv NjBLvGNF2J69dxvMrSZXwx1FfemP3Zk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-260-Q4AVGFAoNCuvO8_eHBIvbQ-1; Wed, 31 Mar 2021 03:34:52 -0400 X-MC-Unique: Q4AVGFAoNCuvO8_eHBIvbQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 87C43108BD09; Wed, 31 Mar 2021 07:34:50 +0000 (UTC) Received: from [10.36.113.60] (ovpn-113-60.ams2.redhat.com [10.36.113.60]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5582D5C5AE; Wed, 31 Mar 2021 07:34:45 +0000 (UTC) To: Catalin Marinas , Steven Price 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 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> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH v10 2/6] arm64: kvm: Introduce MTE VM feature Message-ID: <8977120b-841d-4882-2472-6e403bc9c797@redhat.com> Date: Wed, 31 Mar 2021 09:34:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210330103013.GD18075@arm.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210331_083459_401778_FD02ADA5 X-CRM114-Status: GOOD ( 41.21 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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. > > 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. 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" > > For user MTE, we get away with this as the MAP_ANONYMOUS requirement > would filter it out while arch_add_memory() will ensure it's mapped as > untagged in the linear map. See another recent fix for hotplugged > memory: d15dfd31384b ("arm64: mte: Map hotplugged memory as Normal > Tagged"). We needed to ensure that ZONE_DEVICE doesn't end up as tagged, > only hoplugged memory. Both handled via arch_add_memory() in the arch > code with ZONE_DEVICE starting at devm_memremap_pages(). > >>>> 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. >> >> I certainly hope this is the case - it's the weird corner cases of device >> drivers that worry me. E.g. I know i915 has a "hidden" mmap behind an ioctl >> (see i915_gem_mmap_ioctl(), although this case is fine - it's MAP_SHARED). >> Mali's kbase did something similar in the past. > > I think this should be fine since it's not a MAP_ANONYMOUS (we do allow > MAP_SHARED to be tagged). > -- Thanks, David / dhildenb _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel