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,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 2F5D2C433B4 for ; Tue, 4 May 2021 15:40:49 +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 8BD58611AB for ; Tue, 4 May 2021 15:40:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8BD58611AB 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]:54618 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ldxAF-0006g9-Dq for qemu-devel@archiver.kernel.org; Tue, 04 May 2021 11:40:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44600) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ldwze-0004Rh-P2 for qemu-devel@nongnu.org; Tue, 04 May 2021 11:29:50 -0400 Received: from mail.kernel.org ([198.145.29.99]:47044) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ldwzc-0001vM-NK for qemu-devel@nongnu.org; Tue, 04 May 2021 11:29:50 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 1BDA060FDC; Tue, 4 May 2021 15:29:42 +0000 (UTC) Date: Tue, 4 May 2021 16:29:40 +0100 From: Catalin Marinas To: Steven Price Subject: Re: [PATCH v11 1/6] arm64: mte: Sync tags for pages where PTE is untagged Message-ID: <20210504152938.GC8078@arm.com> References: <20210416154309.22129-1-steven.price@arm.com> <20210416154309.22129-2-steven.price@arm.com> <20210427174357.GA17872@arm.com> <0ab0017c-1eaf-201e-587f-101e03da6b80@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0ab0017c-1eaf-201e-587f-101e03da6b80@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Received-SPF: pass client-ip=198.145.29.99; envelope-from=cmarinas@kernel.org; helo=mail.kernel.org X-Spam_score_int: -66 X-Spam_score: -6.7 X-Spam_bar: ------ X-Spam_report: (-6.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.248, RCVD_IN_DNSWL_HI=-5, 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 Thu, Apr 29, 2021 at 05:06:05PM +0100, Steven Price wrote: > On 27/04/2021 18:43, Catalin Marinas wrote: > > On Fri, Apr 16, 2021 at 04:43:04PM +0100, Steven Price wrote: > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > > > index e17b96d0e4b5..cf4b52a33b3c 100644 > > > --- a/arch/arm64/include/asm/pgtable.h > > > +++ b/arch/arm64/include/asm/pgtable.h > > > @@ -312,7 +312,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, > > > __sync_icache_dcache(pte); > > > if (system_supports_mte() && > > > - pte_present(pte) && pte_tagged(pte) && !pte_special(pte)) > > > + pte_present(pte) && (pte_val(pte) & PTE_USER) && !pte_special(pte)) > > > > I would add a pte_user() macro here or, if we restore the tags only when > > the page is readable, use pte_access_permitted(pte, false). Also add a > > comment why we do this. > > pte_access_permitted() looks like it describes what we want (user space can > access the memory). I'll add the following comment: > > /* > * If the PTE would provide user space will access to the tags I think drop "will". > * associated with it then ensure that the MTE tags are synchronised. > * Exec-only mappings don't expose tags (instruction fetches don't > * check tags). > */ Sounds fine. > > There's also the pte_user_exec() case which may not have the PTE_USER > > set (exec-only permission) but I don't think it matters. We don't do tag > > checking on instruction fetches, so if the user adds a PROT_READ to it, > > it would go through set_pte_at() again. I'm not sure KVM does anything > > special with exec-only mappings at stage 2, I suspect they won't be > > accessible by the guest (but needs checking). > > It comes down to the behaviour of get_user_pages(). AFAICT that will fail if > the memory is exec-only, so no stage 2 mapping will be created. Which of > course means the guest can't do anything with that memory. That certainly > seems like the only sane behaviour even without MTE. That's my understanding as well. The get_user_pages_fast() path uses pte_access_permitted() and should return false. The slower get_user_pages() relies on checking the vma flags and it checks for VM_READ. -- Catalin