From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CD0C51534E9; Mon, 28 Oct 2024 18:09:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730138949; cv=none; b=Q9fEQF8fHoi7PgCnxgEJKKl2TB0fivHwXqBtCQ4ObkLgGvf2ChOVRFKueqbCaHCsJNhhSvBKhbnz5djY2Ts2WDBasv1SaR7LtcOwT7a5zRCVphV2TETXHa7QiwxpAcPLObfKzN3OqPxjq3I5xFlIbCuiHUjOgw3jxH+2PFyViB0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730138949; c=relaxed/simple; bh=CeJEGSCNf1EsllIQYit4ccvKZkgbLPbEtbyLPC5vn2k=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=tNqWVIKvu5ib+DH81OoAn5W/mZICcCbwgneu8z+gdaL0Oz/+3rGjUE0WTMdo77rNUBCwrVClA9PIZH6Kb0s+qjwG1hfEVhRKIIcmud4gjCh7lteRzxds+L/y3cz/Q7jKITbJGyvqMJLCi2VKdGS51TVWm71rPS4D+Ceq/UViQQ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aAlxneXY; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="aAlxneXY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4F046C4CEC3; Mon, 28 Oct 2024 18:09:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1730138949; bh=CeJEGSCNf1EsllIQYit4ccvKZkgbLPbEtbyLPC5vn2k=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=aAlxneXYuqZQ7bd+tCz2C3V2pCghZNw8UEOSmUD61Sy3RccoFVjz7gTbNHeA6Pb22 hTsZ4eLxayQy2lmBtQHNnvZgzLF+ktY7YmdT+UbbsVqfEyJ1mWkMbk2CPxgE38SDld ikUZ7HTCRvLCTWuZXdrwXMw+F4kA9mfoeBSo4121/cq6QuqsOZMirQlpLTpt0nmKDN ekS2Pi+NkwN+w/ZfHkK80me54SfWsYgSdw1tme8WTd9pa0wa3dR5qEp0mR70wl1T35 iLjuyuOTR/EaaKH0KDSSdf4NMU6pjBTK98p47i2lvvcnRwtvG6VpWSnzpf1dk9H6Gc xqmhOleLZL9sQ== Received: from sofa.misterjones.org ([185.219.108.64] helo=wait-a-minute.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1t5UAs-007fYC-Qq; Mon, 28 Oct 2024 18:09:07 +0000 Date: Mon, 28 Oct 2024 18:09:05 +0000 Message-ID: <87ldy8t7zy.wl-maz@kernel.org> From: Marc Zyngier 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 , Catalin Marinas , Mark Rutland , Oliver Upton , Joey Gouly , Zenghui Yu Subject: Re: [PATCH 3/4] arm64: mte: update code comments In-Reply-To: References: <20241028094014.2596619-1-aneesh.kumar@kernel.org> <20241028094014.2596619-4-aneesh.kumar@kernel.org> <87plnktt2q.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/29.4 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: aneesh.kumar@kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, Suzuki.Poulose@arm.com, steven.price@arm.com, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, oliver.upton@linux.dev, joey.gouly@arm.com, yuzenghui@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Mon, 28 Oct 2024 12:47:30 +0000, Aneesh Kumar K.V wrote: > > >> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > >> index a509b63bd4dd..b5824e93cee0 100644 > >> --- a/arch/arm64/kvm/mmu.c > >> +++ b/arch/arm64/kvm/mmu.c > >> @@ -1390,11 +1390,8 @@ static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva) > >> * 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. > >> * > >> - * The race in the test/set of the PG_mte_tagged flag is handled by: > >> - * - preventing VM_SHARED mappings in a memslot with MTE preventing two VMs > >> - * racing to santise the same page > >> - * - mmap_lock protects between a VM faulting a page in and the VMM performing > >> - * an mprotect() to add VM_MTE > >> + * The race in the test/set of the PG_mte_tagged flag is handled by > >> + * using PG_mte_lock and PG_mte_tagged together. > > > > How? This comment is pretty content-free. TO be useful, you should > > elaborate on *how* these two are used together. > > > > I will add more details described in commit d77e59a8fccde7fb5dd8c57594ed147b4291c970 > Should i quote the commit there in the comment? The commit is not relevant. What is important is an indication of how the race is resolved if that's important. A reference to try_page_mte_tagging() would probably be the right thing to do. > > > > >> */ > >> static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn, > >> unsigned long size) > >> @@ -1646,7 +1643,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > >> } > >> > >> if (!fault_is_perm && !device && kvm_has_mte(kvm)) { > >> - /* Check the VMM hasn't introduced a new disallowed VMA */ > >> + /* > >> + * not a permission fault implies a translation fault which > >> + * means mapping the page for the first time > > > > How about an Access fault due to page ageing? > > > > IIUC access fault is already handled by the caller kvm_handle_guest_abort? > I can add that as part of the updated comments? Maybe. The thing is, you are removing a pretty essential comment for no good reason, and now there is no rational left behind the -EFAULT that is returned. M. -- Without deviation from the norm, progress is not possible.