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,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 64B20C433ED for ; Thu, 20 May 2021 15:58:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 484C761163 for ; Thu, 20 May 2021 15:58:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232919AbhETP73 (ORCPT ); Thu, 20 May 2021 11:59:29 -0400 Received: from foss.arm.com ([217.140.110.172]:54570 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232488AbhETP71 (ORCPT ); Thu, 20 May 2021 11:59:27 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 563B131B; Thu, 20 May 2021 08:58:05 -0700 (PDT) Received: from [192.168.1.179] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 804E03F73B; Thu, 20 May 2021 08:58:02 -0700 (PDT) From: Steven Price Subject: Re: [PATCH v12 7/8] KVM: arm64: ioctl to fetch/store tags in a guest To: Catalin Marinas 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 References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-8-steven.price@arm.com> <20210520120556.GC12251@arm.com> Message-ID: Date: Thu, 20 May 2021 16:58:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210520120556.GC12251@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/05/2021 13:05, Catalin Marinas wrote: > On Mon, May 17, 2021 at 01:32:38PM +0100, Steven Price wrote: >> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h >> index 24223adae150..b3edde68bc3e 100644 >> --- a/arch/arm64/include/uapi/asm/kvm.h >> +++ b/arch/arm64/include/uapi/asm/kvm.h >> @@ -184,6 +184,17 @@ struct kvm_vcpu_events { >> __u32 reserved[12]; >> }; >> >> +struct kvm_arm_copy_mte_tags { >> + __u64 guest_ipa; >> + __u64 length; >> + void __user *addr; >> + __u64 flags; >> + __u64 reserved[2]; > > I forgot the past discussions, what's the reserved for? Future > expansion? Yes - for future expansion. Marc asked for them[1]: > I'd be keen on a couple of reserved __64s. Just in case... [1] https://lore.kernel.org/r/87ft14xl9e.wl-maz%40kernel.org >> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c >> index e89a5e275e25..4b6c83beb75d 100644 >> --- a/arch/arm64/kvm/arm.c >> +++ b/arch/arm64/kvm/arm.c >> @@ -1309,6 +1309,65 @@ static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm, >> } >> } >> >> +static int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >> + struct kvm_arm_copy_mte_tags *copy_tags) >> +{ >> + gpa_t guest_ipa = copy_tags->guest_ipa; >> + size_t length = copy_tags->length; >> + void __user *tags = copy_tags->addr; >> + gpa_t gfn; >> + bool write = !(copy_tags->flags & KVM_ARM_TAGS_FROM_GUEST); >> + int ret = 0; >> + >> + if (copy_tags->reserved[0] || copy_tags->reserved[1]) >> + return -EINVAL; >> + >> + if (copy_tags->flags & ~KVM_ARM_TAGS_FROM_GUEST) >> + return -EINVAL; >> + >> + if (length & ~PAGE_MASK || guest_ipa & ~PAGE_MASK) >> + return -EINVAL; >> + >> + gfn = gpa_to_gfn(guest_ipa); >> + >> + mutex_lock(&kvm->slots_lock); >> + >> + while (length > 0) { >> + kvm_pfn_t pfn = gfn_to_pfn_prot(kvm, gfn, write, NULL); >> + void *maddr; >> + unsigned long num_tags = PAGE_SIZE / MTE_GRANULE_SIZE; >> + >> + if (is_error_noslot_pfn(pfn)) { >> + ret = -EFAULT; >> + goto out; >> + } >> + >> + maddr = page_address(pfn_to_page(pfn)); >> + >> + if (!write) { >> + num_tags = mte_copy_tags_to_user(tags, maddr, num_tags); >> + kvm_release_pfn_clean(pfn); > > Do we need to check if PG_mte_tagged is set? If the page was not faulted > into the guest address space but the VMM has the page, does the > gfn_to_pfn_prot() guarantee that a kvm_set_spte_gfn() was called? If > not, this may read stale tags. Ah, I hadn't thought about that... No I don't believe gfn_to_pfn_prot() will fault it into the guest. >> + } else { >> + num_tags = mte_copy_tags_from_user(maddr, tags, >> + num_tags); >> + kvm_release_pfn_dirty(pfn); >> + } > > Same question here, if the we can't guarantee the stage 2 pte being set, > we'd need to set PG_mte_tagged. This is arguably worse as we'll be writing tags into the guest but without setting PG_mte_tagged - so they'll be lost when the guest then faults the pages in. Which sounds like it should break migration. I think the below should be safe, and avoids the overhead of setting the flag just for reads. Thanks, Steve ----8<---- page = pfn_to_page(pfn); maddr = page_address(page); if (!write) { if (test_bit(PG_mte_tagged, &page->flags)) num_tags = mte_copy_tags_to_user(tags, maddr, MTE_GRANULES_PER_PAGE); else /* No tags in memory, so write zeros */ num_tags = MTE_GRANULES_PER_PAGE - clear_user(tag, MTE_GRANULES_PER_PAGE); kvm_release_pfn_clean(pfn); } else { num_tags = mte_copy_tags_from_user(maddr, tags, MTE_GRANULES_PER_PAGE); kvm_release_pfn_dirty(pfn); } if (num_tags != MTE_GRANULES_PER_PAGE) { ret = -EFAULT; goto out; } if (write) test_and_set_bit(PG_mte_tagged, &page->flags); 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,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 EE489C433ED for ; Thu, 20 May 2021 16:01:19 +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 84EA16108D for ; Thu, 20 May 2021 16:01:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 84EA16108D 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]:32924 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ljl6q-0007tR-Kv for qemu-devel@archiver.kernel.org; Thu, 20 May 2021 12:01:18 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:56036) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ljl3z-0006IR-Mr for qemu-devel@nongnu.org; Thu, 20 May 2021 11:58:20 -0400 Received: from foss.arm.com ([217.140.110.172]:47230) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ljl3n-0005bU-EP for qemu-devel@nongnu.org; Thu, 20 May 2021 11:58:16 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 563B131B; Thu, 20 May 2021 08:58:05 -0700 (PDT) Received: from [192.168.1.179] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 804E03F73B; Thu, 20 May 2021 08:58:02 -0700 (PDT) From: Steven Price Subject: Re: [PATCH v12 7/8] KVM: arm64: ioctl to fetch/store tags in a guest To: Catalin Marinas References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-8-steven.price@arm.com> <20210520120556.GC12251@arm.com> Message-ID: Date: Thu, 20 May 2021 16:58:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210520120556.GC12251@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=217.140.110.172; envelope-from=steven.price@arm.com; helo=foss.arm.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_MED=-2.3, 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 20/05/2021 13:05, Catalin Marinas wrote: > On Mon, May 17, 2021 at 01:32:38PM +0100, Steven Price wrote: >> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h >> index 24223adae150..b3edde68bc3e 100644 >> --- a/arch/arm64/include/uapi/asm/kvm.h >> +++ b/arch/arm64/include/uapi/asm/kvm.h >> @@ -184,6 +184,17 @@ struct kvm_vcpu_events { >> __u32 reserved[12]; >> }; >> >> +struct kvm_arm_copy_mte_tags { >> + __u64 guest_ipa; >> + __u64 length; >> + void __user *addr; >> + __u64 flags; >> + __u64 reserved[2]; > > I forgot the past discussions, what's the reserved for? Future > expansion? Yes - for future expansion. Marc asked for them[1]: > I'd be keen on a couple of reserved __64s. Just in case... [1] https://lore.kernel.org/r/87ft14xl9e.wl-maz%40kernel.org >> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c >> index e89a5e275e25..4b6c83beb75d 100644 >> --- a/arch/arm64/kvm/arm.c >> +++ b/arch/arm64/kvm/arm.c >> @@ -1309,6 +1309,65 @@ static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm, >> } >> } >> >> +static int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >> + struct kvm_arm_copy_mte_tags *copy_tags) >> +{ >> + gpa_t guest_ipa = copy_tags->guest_ipa; >> + size_t length = copy_tags->length; >> + void __user *tags = copy_tags->addr; >> + gpa_t gfn; >> + bool write = !(copy_tags->flags & KVM_ARM_TAGS_FROM_GUEST); >> + int ret = 0; >> + >> + if (copy_tags->reserved[0] || copy_tags->reserved[1]) >> + return -EINVAL; >> + >> + if (copy_tags->flags & ~KVM_ARM_TAGS_FROM_GUEST) >> + return -EINVAL; >> + >> + if (length & ~PAGE_MASK || guest_ipa & ~PAGE_MASK) >> + return -EINVAL; >> + >> + gfn = gpa_to_gfn(guest_ipa); >> + >> + mutex_lock(&kvm->slots_lock); >> + >> + while (length > 0) { >> + kvm_pfn_t pfn = gfn_to_pfn_prot(kvm, gfn, write, NULL); >> + void *maddr; >> + unsigned long num_tags = PAGE_SIZE / MTE_GRANULE_SIZE; >> + >> + if (is_error_noslot_pfn(pfn)) { >> + ret = -EFAULT; >> + goto out; >> + } >> + >> + maddr = page_address(pfn_to_page(pfn)); >> + >> + if (!write) { >> + num_tags = mte_copy_tags_to_user(tags, maddr, num_tags); >> + kvm_release_pfn_clean(pfn); > > Do we need to check if PG_mte_tagged is set? If the page was not faulted > into the guest address space but the VMM has the page, does the > gfn_to_pfn_prot() guarantee that a kvm_set_spte_gfn() was called? If > not, this may read stale tags. Ah, I hadn't thought about that... No I don't believe gfn_to_pfn_prot() will fault it into the guest. >> + } else { >> + num_tags = mte_copy_tags_from_user(maddr, tags, >> + num_tags); >> + kvm_release_pfn_dirty(pfn); >> + } > > Same question here, if the we can't guarantee the stage 2 pte being set, > we'd need to set PG_mte_tagged. This is arguably worse as we'll be writing tags into the guest but without setting PG_mte_tagged - so they'll be lost when the guest then faults the pages in. Which sounds like it should break migration. I think the below should be safe, and avoids the overhead of setting the flag just for reads. Thanks, Steve ----8<---- page = pfn_to_page(pfn); maddr = page_address(page); if (!write) { if (test_bit(PG_mte_tagged, &page->flags)) num_tags = mte_copy_tags_to_user(tags, maddr, MTE_GRANULES_PER_PAGE); else /* No tags in memory, so write zeros */ num_tags = MTE_GRANULES_PER_PAGE - clear_user(tag, MTE_GRANULES_PER_PAGE); kvm_release_pfn_clean(pfn); } else { num_tags = mte_copy_tags_from_user(maddr, tags, MTE_GRANULES_PER_PAGE); kvm_release_pfn_dirty(pfn); } if (num_tags != MTE_GRANULES_PER_PAGE) { ret = -EFAULT; goto out; } if (write) test_and_set_bit(PG_mte_tagged, &page->flags); 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,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 B4802C433B4 for ; Thu, 20 May 2021 15:58:10 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 2AFDD61163 for ; Thu, 20 May 2021 15:58:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2AFDD61163 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 977E84B58D; Thu, 20 May 2021 11:58:09 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id dMK7TnomsU8B; Thu, 20 May 2021 11:58:08 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 411714B5C7; Thu, 20 May 2021 11:58:08 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 1C06E4B545 for ; Thu, 20 May 2021 11:58:07 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id cxYHCYOc7ZXl for ; Thu, 20 May 2021 11:58:05 -0400 (EDT) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mm01.cs.columbia.edu (Postfix) with ESMTP id C43434B58D for ; Thu, 20 May 2021 11:58:05 -0400 (EDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 563B131B; Thu, 20 May 2021 08:58:05 -0700 (PDT) Received: from [192.168.1.179] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 804E03F73B; Thu, 20 May 2021 08:58:02 -0700 (PDT) From: Steven Price Subject: Re: [PATCH v12 7/8] KVM: arm64: ioctl to fetch/store tags in a guest To: Catalin Marinas References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-8-steven.price@arm.com> <20210520120556.GC12251@arm.com> Message-ID: Date: Thu, 20 May 2021 16:58:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210520120556.GC12251@arm.com> Content-Language: en-GB Cc: "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, Marc Zyngier , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Dave Martin , linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On 20/05/2021 13:05, Catalin Marinas wrote: > On Mon, May 17, 2021 at 01:32:38PM +0100, Steven Price wrote: >> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h >> index 24223adae150..b3edde68bc3e 100644 >> --- a/arch/arm64/include/uapi/asm/kvm.h >> +++ b/arch/arm64/include/uapi/asm/kvm.h >> @@ -184,6 +184,17 @@ struct kvm_vcpu_events { >> __u32 reserved[12]; >> }; >> >> +struct kvm_arm_copy_mte_tags { >> + __u64 guest_ipa; >> + __u64 length; >> + void __user *addr; >> + __u64 flags; >> + __u64 reserved[2]; > > I forgot the past discussions, what's the reserved for? Future > expansion? Yes - for future expansion. Marc asked for them[1]: > I'd be keen on a couple of reserved __64s. Just in case... [1] https://lore.kernel.org/r/87ft14xl9e.wl-maz%40kernel.org >> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c >> index e89a5e275e25..4b6c83beb75d 100644 >> --- a/arch/arm64/kvm/arm.c >> +++ b/arch/arm64/kvm/arm.c >> @@ -1309,6 +1309,65 @@ static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm, >> } >> } >> >> +static int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >> + struct kvm_arm_copy_mte_tags *copy_tags) >> +{ >> + gpa_t guest_ipa = copy_tags->guest_ipa; >> + size_t length = copy_tags->length; >> + void __user *tags = copy_tags->addr; >> + gpa_t gfn; >> + bool write = !(copy_tags->flags & KVM_ARM_TAGS_FROM_GUEST); >> + int ret = 0; >> + >> + if (copy_tags->reserved[0] || copy_tags->reserved[1]) >> + return -EINVAL; >> + >> + if (copy_tags->flags & ~KVM_ARM_TAGS_FROM_GUEST) >> + return -EINVAL; >> + >> + if (length & ~PAGE_MASK || guest_ipa & ~PAGE_MASK) >> + return -EINVAL; >> + >> + gfn = gpa_to_gfn(guest_ipa); >> + >> + mutex_lock(&kvm->slots_lock); >> + >> + while (length > 0) { >> + kvm_pfn_t pfn = gfn_to_pfn_prot(kvm, gfn, write, NULL); >> + void *maddr; >> + unsigned long num_tags = PAGE_SIZE / MTE_GRANULE_SIZE; >> + >> + if (is_error_noslot_pfn(pfn)) { >> + ret = -EFAULT; >> + goto out; >> + } >> + >> + maddr = page_address(pfn_to_page(pfn)); >> + >> + if (!write) { >> + num_tags = mte_copy_tags_to_user(tags, maddr, num_tags); >> + kvm_release_pfn_clean(pfn); > > Do we need to check if PG_mte_tagged is set? If the page was not faulted > into the guest address space but the VMM has the page, does the > gfn_to_pfn_prot() guarantee that a kvm_set_spte_gfn() was called? If > not, this may read stale tags. Ah, I hadn't thought about that... No I don't believe gfn_to_pfn_prot() will fault it into the guest. >> + } else { >> + num_tags = mte_copy_tags_from_user(maddr, tags, >> + num_tags); >> + kvm_release_pfn_dirty(pfn); >> + } > > Same question here, if the we can't guarantee the stage 2 pte being set, > we'd need to set PG_mte_tagged. This is arguably worse as we'll be writing tags into the guest but without setting PG_mte_tagged - so they'll be lost when the guest then faults the pages in. Which sounds like it should break migration. I think the below should be safe, and avoids the overhead of setting the flag just for reads. Thanks, Steve ----8<---- page = pfn_to_page(pfn); maddr = page_address(page); if (!write) { if (test_bit(PG_mte_tagged, &page->flags)) num_tags = mte_copy_tags_to_user(tags, maddr, MTE_GRANULES_PER_PAGE); else /* No tags in memory, so write zeros */ num_tags = MTE_GRANULES_PER_PAGE - clear_user(tag, MTE_GRANULES_PER_PAGE); kvm_release_pfn_clean(pfn); } else { num_tags = mte_copy_tags_from_user(maddr, tags, MTE_GRANULES_PER_PAGE); kvm_release_pfn_dirty(pfn); } if (num_tags != MTE_GRANULES_PER_PAGE) { ret = -EFAULT; goto out; } if (write) test_and_set_bit(PG_mte_tagged, &page->flags); _______________________________________________ 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=-10.6 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 EA13EC433ED for ; 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Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210520120556.GC12251@arm.com> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210520_085808_817127_5B2BF09B X-CRM114-Status: GOOD ( 24.71 ) 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 20/05/2021 13:05, Catalin Marinas wrote: > On Mon, May 17, 2021 at 01:32:38PM +0100, Steven Price wrote: >> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h >> index 24223adae150..b3edde68bc3e 100644 >> --- a/arch/arm64/include/uapi/asm/kvm.h >> +++ b/arch/arm64/include/uapi/asm/kvm.h >> @@ -184,6 +184,17 @@ struct kvm_vcpu_events { >> __u32 reserved[12]; >> }; >> >> +struct kvm_arm_copy_mte_tags { >> + __u64 guest_ipa; >> + __u64 length; >> + void __user *addr; >> + __u64 flags; >> + __u64 reserved[2]; > > I forgot the past discussions, what's the reserved for? Future > expansion? Yes - for future expansion. Marc asked for them[1]: > I'd be keen on a couple of reserved __64s. Just in case... [1] https://lore.kernel.org/r/87ft14xl9e.wl-maz%40kernel.org >> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c >> index e89a5e275e25..4b6c83beb75d 100644 >> --- a/arch/arm64/kvm/arm.c >> +++ b/arch/arm64/kvm/arm.c >> @@ -1309,6 +1309,65 @@ static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm, >> } >> } >> >> +static int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >> + struct kvm_arm_copy_mte_tags *copy_tags) >> +{ >> + gpa_t guest_ipa = copy_tags->guest_ipa; >> + size_t length = copy_tags->length; >> + void __user *tags = copy_tags->addr; >> + gpa_t gfn; >> + bool write = !(copy_tags->flags & KVM_ARM_TAGS_FROM_GUEST); >> + int ret = 0; >> + >> + if (copy_tags->reserved[0] || copy_tags->reserved[1]) >> + return -EINVAL; >> + >> + if (copy_tags->flags & ~KVM_ARM_TAGS_FROM_GUEST) >> + return -EINVAL; >> + >> + if (length & ~PAGE_MASK || guest_ipa & ~PAGE_MASK) >> + return -EINVAL; >> + >> + gfn = gpa_to_gfn(guest_ipa); >> + >> + mutex_lock(&kvm->slots_lock); >> + >> + while (length > 0) { >> + kvm_pfn_t pfn = gfn_to_pfn_prot(kvm, gfn, write, NULL); >> + void *maddr; >> + unsigned long num_tags = PAGE_SIZE / MTE_GRANULE_SIZE; >> + >> + if (is_error_noslot_pfn(pfn)) { >> + ret = -EFAULT; >> + goto out; >> + } >> + >> + maddr = page_address(pfn_to_page(pfn)); >> + >> + if (!write) { >> + num_tags = mte_copy_tags_to_user(tags, maddr, num_tags); >> + kvm_release_pfn_clean(pfn); > > Do we need to check if PG_mte_tagged is set? If the page was not faulted > into the guest address space but the VMM has the page, does the > gfn_to_pfn_prot() guarantee that a kvm_set_spte_gfn() was called? If > not, this may read stale tags. Ah, I hadn't thought about that... No I don't believe gfn_to_pfn_prot() will fault it into the guest. >> + } else { >> + num_tags = mte_copy_tags_from_user(maddr, tags, >> + num_tags); >> + kvm_release_pfn_dirty(pfn); >> + } > > Same question here, if the we can't guarantee the stage 2 pte being set, > we'd need to set PG_mte_tagged. This is arguably worse as we'll be writing tags into the guest but without setting PG_mte_tagged - so they'll be lost when the guest then faults the pages in. Which sounds like it should break migration. I think the below should be safe, and avoids the overhead of setting the flag just for reads. Thanks, Steve ----8<---- page = pfn_to_page(pfn); maddr = page_address(page); if (!write) { if (test_bit(PG_mte_tagged, &page->flags)) num_tags = mte_copy_tags_to_user(tags, maddr, MTE_GRANULES_PER_PAGE); else /* No tags in memory, so write zeros */ num_tags = MTE_GRANULES_PER_PAGE - clear_user(tag, MTE_GRANULES_PER_PAGE); kvm_release_pfn_clean(pfn); } else { num_tags = mte_copy_tags_from_user(maddr, tags, MTE_GRANULES_PER_PAGE); kvm_release_pfn_dirty(pfn); } if (num_tags != MTE_GRANULES_PER_PAGE) { ret = -EFAULT; goto out; } if (write) test_and_set_bit(PG_mte_tagged, &page->flags); _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel