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 D40CAC433ED for ; Wed, 19 May 2021 18:06:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B068361355 for ; Wed, 19 May 2021 18:06:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231173AbhESSHh (ORCPT ); Wed, 19 May 2021 14:07:37 -0400 Received: from mail.kernel.org ([198.145.29.99]:33646 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230023AbhESSHg (ORCPT ); Wed, 19 May 2021 14:07:36 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9D76D611BF; Wed, 19 May 2021 18:06:13 +0000 (UTC) Date: Wed, 19 May 2021 19:06:10 +0100 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 v12 3/8] arm64: mte: Sync tags for pages where PTE is untagged Message-ID: <20210519180610.GE21619@arm.com> References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-4-steven.price@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210517123239.8025-4-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 On Mon, May 17, 2021 at 01:32:34PM +0100, 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 for which pte_access_permitted() returns false > as these will not have been swapped out. > > Signed-off-by: Steven Price > --- > arch/arm64/include/asm/pgtable.h | 9 +++++++-- > arch/arm64/kernel/mte.c | 16 ++++++++++++++-- > 2 files changed, 21 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 0b10204e72fc..275178a810c1 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -314,8 +314,13 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, > if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte)) > __sync_icache_dcache(pte); > > - if (system_supports_mte() && > - pte_present(pte) && pte_tagged(pte) && !pte_special(pte)) > + /* > + * If the PTE would provide user space access to the tags associated > + * with it then ensure that the MTE tags are synchronised. Exec-only > + * mappings don't expose tags (instruction fetches don't check tags). > + */ > + if (system_supports_mte() && pte_present(pte) && > + pte_access_permitted(pte, false) && !pte_special(pte)) > mte_sync_tags(ptep, pte); Looking at the mte_sync_page_tags() logic, we bail out early if it's the old pte is not a swap one and the new pte is not tagged. So we only need to call mte_sync_tags() if it's a tagged new pte or the old one is swap. What about changing the set_pte_at() test to: if (system_supports_mte() && pte_present(pte) && !pte_special(pte) && (pte_tagged(pte) || is_swap_pte(READ_ONCE(*ptep)))) mte_sync_tags(ptep, pte); We can even change mte_sync_tags() to take the old pte directly: if (system_supports_mte() && pte_present(pte) && !pte_special(pte)) { pte_t old_pte = READ_ONCE(*ptep); if (pte_tagged(pte) || is_swap_pte(old_pte)) mte_sync_tags(old_pte, pte); } It would save a function call in most cases where the page is not tagged. -- Catalin