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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 328E0C02180 for ; Mon, 13 Jan 2025 19:11:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=N545VQJ4bn+y0pSdJjf/mDvicZgnxEN0HYSjLOeVRco=; b=SgMRtGLQ+hY+UQQlfVBdcNjkyo DMAhplfa5Jl1Ww9UKeCte9DA5/g4GnG4E97Zn6jssGy2weSgFXT4Gl3QSTFZDBRp4Fiso5Kbg0UUL zsHRdVv/uN3OnNf2xvXEYTPE8Rs17x/JFGBEpfPM0pph3LmhMWdaTX3mvsVkzAbi+DCVcPRoPwLcr 3y3GJrQuXNMCtBAH+TZUWRZnE9Svx2OSH6nCH8/XWo9z2QjIebDo5lfwU/uuLAEX/4oq6m7RPv6tz NKAG8HZV/iXmoeh2u+gRG+3W2gAHDbk+65So1HfTIJDWGozj74qgk/IEgg8AooD+BmbjCJ/I0dtg/ AcZh8iFA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tXPpp-00000006KUB-3rjC; Mon, 13 Jan 2025 19:10:49 +0000 Received: from nyc.source.kernel.org ([147.75.193.91]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tXPoa-00000006KH2-3NsK for linux-arm-kernel@lists.infradead.org; Mon, 13 Jan 2025 19:09:34 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by nyc.source.kernel.org (Postfix) with ESMTP id 5A2CBA40BA4; Mon, 13 Jan 2025 19:07:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB76EC4CED6; Mon, 13 Jan 2025 19:09:28 +0000 (UTC) Date: Mon, 13 Jan 2025 19:09:26 +0000 From: Catalin Marinas To: "Aneesh Kumar K.V" Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, Suzuki K Poulose , Steven Price , Will Deacon , Marc Zyngier , Mark Rutland , Oliver Upton , Joey Gouly , Zenghui Yu , Peter Collingbourne Subject: Re: [PATCH v2 5/7] KVM: arm64: MTE: Use stage-2 NoTagAccess memory attribute if supported Message-ID: References: <20250110110023.2963795-1-aneesh.kumar@kernel.org> <20250110110023.2963795-6-aneesh.kumar@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250113_110932_913129_CD9ABAB2 X-CRM114-Status: GOOD ( 24.18 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sat, Jan 11, 2025 at 06:49:55PM +0530, Aneesh Kumar K.V wrote: > Catalin Marinas writes: > > On Fri, Jan 10, 2025 at 04:30:21PM +0530, Aneesh Kumar K.V (Arm) wrote: > >> Currently, the kernel won't start a guest if the MTE feature is enabled > > ... > > >> @@ -2152,7 +2162,8 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, > >> if (!vma) > >> break; > >> > >> - if (kvm_has_mte(kvm) && !kvm_vma_mte_allowed(vma)) { > >> + if (kvm_has_mte(kvm) && > >> + !kvm_has_mte_perm(kvm) && !kvm_vma_mte_allowed(vma)) { > >> ret = -EINVAL; > >> break; > >> } > > > > I don't think we should change this, or at least not how it's done above > > (Suzuki raised a related issue internally relaxing this for VM_PFNMAP). > > > > For standard memory slots, we want to reject them upfront rather than > > deferring to the fault handler. An example here is file mmap() passed as > > standard RAM to the VM. It's an unnecessary change in behaviour IMHO. > > I'd only relax this for VM_PFNMAP mappings further down in this > > function (and move the VM_PFNMAP check above; see Suzuki's internal > > patch, unless he posted it publicly already). > > But we want to handle memslots backed by pagecache pages for virtio-shm > here (virtiofs dax use case). Ah, I forgot about this use case. So with virtiofs DAX, does a host page cache page (host VMM mmap()) get mapped directly into the guest as a separate memory slot? In this case, the host vma would not have VM_MTE_ALLOWED set. > With MTE_PERM, we can essentially skip the > kvm_vma_mte_allowed(vma) check because we handle all types in the fault > handler. This was pretty much the early behaviour when we added KVM support for MTE, allow !VM_MTE_ALLOWED and trap them later. However, we disallowed VM_SHARED because of some non-trivial race. Commit d89585fbb308 ("KVM: arm64: unify the tests for VMAs in memslots when MTE is enabled") changed this behaviour and the VM_MTE_ALLOWED check happens upfront. A subsequent commit removed the VM_SHARED check. It's a minor ABI change but I'm trying to figure out why we needed this upfront check rather than simply dropping the VM_SHARED check. Adding Peter in case he remembers. I can't see any race if we simply skipped this check altogether, irrespective of FEAT_MTE_PERM. -- Catalin