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);