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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 D1D6EC433C1 for ; Fri, 26 Mar 2021 18:57:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 86BB761A13 for ; Fri, 26 Mar 2021 18:57:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230202AbhCZS5W (ORCPT ); Fri, 26 Mar 2021 14:57:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:42976 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230194AbhCZS5A (ORCPT ); Fri, 26 Mar 2021 14:57:00 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9F6AA619F7; Fri, 26 Mar 2021 18:56:56 +0000 (UTC) Date: Fri, 26 Mar 2021 18:56:54 +0000 From: Catalin Marinas To: Steven Price 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 Subject: Re: [PATCH v10 1/6] arm64: mte: Sync tags for pages where PTE is untagged Message-ID: <20210326185653.GG5126@arm.com> References: <20210312151902.17853-1-steven.price@arm.com> <20210312151902.17853-2-steven.price@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210312151902.17853-2-steven.price@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steven, On Fri, Mar 12, 2021 at 03:18:57PM +0000, Steven Price wrote: > A KVM guest could store tags in a page even if the VMM hasn't mapped > the page with PROT_MTE. So when restoring pages from swap we will > need to check to see if there are any saved tags even if !pte_tagged(). > > However don't check pages which are !pte_valid_user() as these will > not have been swapped out. > > Signed-off-by: Steven Price > --- > arch/arm64/include/asm/pgtable.h | 2 +- > arch/arm64/kernel/mte.c | 16 ++++++++++++---- > 2 files changed, 13 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index e17b96d0e4b5..84166625c989 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_valid_user(pte) && !pte_special(pte)) > mte_sync_tags(ptep, pte); With the EPAN patches queued in for-next/epan, pte_valid_user() disappeared as its semantics weren't very clear. So this relies on the set_pte_at() being done on the VMM address space. I wonder, if the VMM did an mprotect(PROT_NONE), can the VM still access it via stage 2? If yes, the pte_valid_user() test wouldn't work. We need something like pte_present() && addr <= user_addr_max(). BTW, ignoring virtualisation, can we ever bring a page in from swap on a PROT_NONE mapping (say fault-around)? It's not too bad if we keep the metadata around for when the pte becomes accessible but I suspect we remove it if the page is removed from swap. -- Catalin