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=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 64C38C433B4 for ; Tue, 27 Apr 2021 17:44:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 38531613EA for ; Tue, 27 Apr 2021 17:44:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236019AbhD0Ros (ORCPT ); Tue, 27 Apr 2021 13:44:48 -0400 Received: from mail.kernel.org ([198.145.29.99]:49796 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238296AbhD0Roq (ORCPT ); Tue, 27 Apr 2021 13:44:46 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 81EE6613E5; Tue, 27 Apr 2021 17:44:00 +0000 (UTC) Date: Tue, 27 Apr 2021 18:43:58 +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 v11 1/6] arm64: mte: Sync tags for pages where PTE is untagged Message-ID: <20210427174357.GA17872@arm.com> References: <20210416154309.22129-1-steven.price@arm.com> <20210416154309.22129-2-steven.price@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210416154309.22129-2-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 On Fri, Apr 16, 2021 at 04:43:04PM +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 which are !pte_valid_user() as these will > not have been swapped out. You should remove the pte_valid_user() mention from the commit log as well. > 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. 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). > mte_sync_tags(ptep, pte); > > __check_racy_pte_update(mm, ptep, pte); > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index b3c70a612c7a..e016ab57ea36 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -26,17 +26,23 @@ u64 gcr_kernel_excl __ro_after_init; > > static bool report_fault_once = true; > > -static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > +static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap, > + bool pte_is_tagged) > { > pte_t old_pte = READ_ONCE(*ptep); > > if (check_swap && is_swap_pte(old_pte)) { > swp_entry_t entry = pte_to_swp_entry(old_pte); > > - if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) > + if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) { > + set_bit(PG_mte_tagged, &page->flags); > return; > + } > } > > + if (!pte_is_tagged || test_and_set_bit(PG_mte_tagged, &page->flags)) > + return; I don't think we need another test_bit() here, it was done in the caller (bar potential races which need more thought). > + > page_kasan_tag_reset(page); > /* > * We need smp_wmb() in between setting the flags and clearing the > @@ -54,11 +60,13 @@ void mte_sync_tags(pte_t *ptep, pte_t pte) > struct page *page = pte_page(pte); > long i, nr_pages = compound_nr(page); > bool check_swap = nr_pages == 1; > + bool pte_is_tagged = pte_tagged(pte); > > /* if PG_mte_tagged is set, tags have already been initialised */ > for (i = 0; i < nr_pages; i++, page++) { > - if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > - mte_sync_page_tags(page, ptep, check_swap); > + if (!test_bit(PG_mte_tagged, &page->flags)) > + mte_sync_page_tags(page, ptep, check_swap, > + pte_is_tagged); > } > } You were right in the previous thread that if we have a race, it's already there even without your patches KVM patches. If it's the same pte in a multithreaded app, we should be ok as the core code holds the ptl (the arch code also holds the mmap_lock during exception handling but only as a reader, so you can have multiple holders). If there are multiple ptes to the same page, for example mapped with MAP_ANONYMOUS | MAP_SHARED, metadata recovery is done via arch_swap_restore() before we even set the pte and with the page locked. So calling lock_page() again in mte_restore_tags() would deadlock. I can see that do_swap_page() also holds the page lock around set_pte_at(), so I think we are covered. Any other scenario I may have missed? My understanding is that if the pte is the same, we have the ptl. Otherwise we have the page lock for shared pages. -- Catalin 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 F1387C43461 for ; Tue, 27 Apr 2021 17:50:29 +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 71965613F3 for ; Tue, 27 Apr 2021 17:50:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 71965613F3 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]:51630 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lbRqu-0003Sp-Ee for qemu-devel@archiver.kernel.org; Tue, 27 Apr 2021 13:50:28 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45762) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lbRks-0008Ex-G6 for qemu-devel@nongnu.org; Tue, 27 Apr 2021 13:44:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:38498) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lbRkk-0007vg-GU for qemu-devel@nongnu.org; Tue, 27 Apr 2021 13:44:13 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 81EE6613E5; Tue, 27 Apr 2021 17:44:00 +0000 (UTC) Date: Tue, 27 Apr 2021 18:43:58 +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: <20210427174357.GA17872@arm.com> References: <20210416154309.22129-1-steven.price@arm.com> <20210416154309.22129-2-steven.price@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210416154309.22129-2-steven.price@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=0.249, 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 Fri, Apr 16, 2021 at 04:43:04PM +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 which are !pte_valid_user() as these will > not have been swapped out. You should remove the pte_valid_user() mention from the commit log as well. > 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. 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). > mte_sync_tags(ptep, pte); > > __check_racy_pte_update(mm, ptep, pte); > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index b3c70a612c7a..e016ab57ea36 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -26,17 +26,23 @@ u64 gcr_kernel_excl __ro_after_init; > > static bool report_fault_once = true; > > -static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > +static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap, > + bool pte_is_tagged) > { > pte_t old_pte = READ_ONCE(*ptep); > > if (check_swap && is_swap_pte(old_pte)) { > swp_entry_t entry = pte_to_swp_entry(old_pte); > > - if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) > + if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) { > + set_bit(PG_mte_tagged, &page->flags); > return; > + } > } > > + if (!pte_is_tagged || test_and_set_bit(PG_mte_tagged, &page->flags)) > + return; I don't think we need another test_bit() here, it was done in the caller (bar potential races which need more thought). > + > page_kasan_tag_reset(page); > /* > * We need smp_wmb() in between setting the flags and clearing the > @@ -54,11 +60,13 @@ void mte_sync_tags(pte_t *ptep, pte_t pte) > struct page *page = pte_page(pte); > long i, nr_pages = compound_nr(page); > bool check_swap = nr_pages == 1; > + bool pte_is_tagged = pte_tagged(pte); > > /* if PG_mte_tagged is set, tags have already been initialised */ > for (i = 0; i < nr_pages; i++, page++) { > - if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > - mte_sync_page_tags(page, ptep, check_swap); > + if (!test_bit(PG_mte_tagged, &page->flags)) > + mte_sync_page_tags(page, ptep, check_swap, > + pte_is_tagged); > } > } You were right in the previous thread that if we have a race, it's already there even without your patches KVM patches. If it's the same pte in a multithreaded app, we should be ok as the core code holds the ptl (the arch code also holds the mmap_lock during exception handling but only as a reader, so you can have multiple holders). If there are multiple ptes to the same page, for example mapped with MAP_ANONYMOUS | MAP_SHARED, metadata recovery is done via arch_swap_restore() before we even set the pte and with the page locked. So calling lock_page() again in mte_restore_tags() would deadlock. I can see that do_swap_page() also holds the page lock around set_pte_at(), so I think we are covered. Any other scenario I may have missed? My understanding is that if the pte is the same, we have the ptl. Otherwise we have the page lock for shared pages. -- Catalin 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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 3B443C433B4 for ; Tue, 27 Apr 2021 17:44:10 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id AAAF3613C0 for ; Tue, 27 Apr 2021 17:44:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AAAF3613C0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 37F9E4B162; Tue, 27 Apr 2021 13:44:09 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id lrPnVF8o-Ty1; Tue, 27 Apr 2021 13:44:07 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id C360A4B194; Tue, 27 Apr 2021 13:44:07 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 262094B194 for ; Tue, 27 Apr 2021 13:44:06 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id JKlmu6p0MNIg for ; Tue, 27 Apr 2021 13:44:04 -0400 (EDT) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id A5BB34B187 for ; Tue, 27 Apr 2021 13:44:04 -0400 (EDT) Received: by mail.kernel.org (Postfix) with ESMTPSA id 81EE6613E5; Tue, 27 Apr 2021 17:44:00 +0000 (UTC) Date: Tue, 27 Apr 2021 18:43:58 +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: <20210427174357.GA17872@arm.com> References: <20210416154309.22129-1-steven.price@arm.com> <20210416154309.22129-2-steven.price@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210416154309.22129-2-steven.price@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Cc: "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, Marc Zyngier , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Dave Martin , linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Fri, Apr 16, 2021 at 04:43:04PM +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 which are !pte_valid_user() as these will > not have been swapped out. You should remove the pte_valid_user() mention from the commit log as well. > 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. 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). > mte_sync_tags(ptep, pte); > > __check_racy_pte_update(mm, ptep, pte); > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index b3c70a612c7a..e016ab57ea36 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -26,17 +26,23 @@ u64 gcr_kernel_excl __ro_after_init; > > static bool report_fault_once = true; > > -static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > +static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap, > + bool pte_is_tagged) > { > pte_t old_pte = READ_ONCE(*ptep); > > if (check_swap && is_swap_pte(old_pte)) { > swp_entry_t entry = pte_to_swp_entry(old_pte); > > - if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) > + if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) { > + set_bit(PG_mte_tagged, &page->flags); > return; > + } > } > > + if (!pte_is_tagged || test_and_set_bit(PG_mte_tagged, &page->flags)) > + return; I don't think we need another test_bit() here, it was done in the caller (bar potential races which need more thought). > + > page_kasan_tag_reset(page); > /* > * We need smp_wmb() in between setting the flags and clearing the > @@ -54,11 +60,13 @@ void mte_sync_tags(pte_t *ptep, pte_t pte) > struct page *page = pte_page(pte); > long i, nr_pages = compound_nr(page); > bool check_swap = nr_pages == 1; > + bool pte_is_tagged = pte_tagged(pte); > > /* if PG_mte_tagged is set, tags have already been initialised */ > for (i = 0; i < nr_pages; i++, page++) { > - if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > - mte_sync_page_tags(page, ptep, check_swap); > + if (!test_bit(PG_mte_tagged, &page->flags)) > + mte_sync_page_tags(page, ptep, check_swap, > + pte_is_tagged); > } > } You were right in the previous thread that if we have a race, it's already there even without your patches KVM patches. If it's the same pte in a multithreaded app, we should be ok as the core code holds the ptl (the arch code also holds the mmap_lock during exception handling but only as a reader, so you can have multiple holders). If there are multiple ptes to the same page, for example mapped with MAP_ANONYMOUS | MAP_SHARED, metadata recovery is done via arch_swap_restore() before we even set the pte and with the page locked. So calling lock_page() again in mte_restore_tags() would deadlock. I can see that do_swap_page() also holds the page lock around set_pte_at(), so I think we are covered. Any other scenario I may have missed? My understanding is that if the pte is the same, we have the ptl. Otherwise we have the page lock for shared pages. -- Catalin _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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=-10.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 4DE0DC43460 for ; Tue, 27 Apr 2021 17:46:11 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 C8B93613BD for ; Tue, 27 Apr 2021 17:46:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C8B93613BD Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=X5Asq2Yr2Vt8OMn1bg3LiblpNkVrs6ZLVr9Xe64fVPU=; b=UA0EZCSjx4iwpfSdofOMJcn5O 4+kMlOarlH28aIGtoA9dDlEBdRZO5QzTwYj8VBUNqca64TTYMMsh2qjH4LlTWe2vYGUsJu4l6zOH7 ZZxESa6IdkNi849wWAezjwFNbyDEp9+WmLy4cvxSKPnkZZynZXk6sQZWHU9gNKBT9ljIJmykIWleh AQUMEAl9+CT5ECX97McCixcOwvifDAtk/kYREwMBXoYR5jrUctcSrJCBKDSj+i899YeWx0SeDiv98 07vno21b+7lVkU/e43rsFvPzWTyTBnwntWoKvzBF9+grKjahH4p/QS9Aj/7AGH7zpCW4GNqKpxvMp hHQA61M4A==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lbRkq-001yfv-3d; Tue, 27 Apr 2021 17:44:12 +0000 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lbRkn-001yfk-WC for linux-arm-kernel@desiato.infradead.org; Tue, 27 Apr 2021 17:44:10 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=4f7N/1nTbrUdGMbAqBvFaJd/6tr9bz4qF349gnYkGSQ=; b=HcXBxgsWhsekHnSrKdfb5f+pQh +h4T3r40Eiaj6vb6HFp2dLgUqactHiV1SbFYWLYg0PO7lU0cKwc5HLlFG4vD7FYnUHdAk0scO4RJy f7sp18LbJZzX7uvXizZQjBvtBYQXdz33PDzlvuBC2FhxmUq48scWaiadoaC0Qdby+EMudpaS18hzu afij1LIcEJCt03n9FdtnLXlokhZaj1ei5dwNJDLPeL24XDjhcWS1smgY6Qs3MExVWZfLRvvQ0/tGP mbFAZmCLOoCVPxDjMINCcOYfGx4S9cl0ex66VjGWh3UiHJYFAUj6/b0XUBID+gqsoyHIjCLJP+tED AprJVEmA==; Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lbRkj-00GtXI-CV for linux-arm-kernel@lists.infradead.org; Tue, 27 Apr 2021 17:44:06 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 81EE6613E5; Tue, 27 Apr 2021 17:44:00 +0000 (UTC) Date: Tue, 27 Apr 2021 18:43:58 +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 v11 1/6] arm64: mte: Sync tags for pages where PTE is untagged Message-ID: <20210427174357.GA17872@arm.com> References: <20210416154309.22129-1-steven.price@arm.com> <20210416154309.22129-2-steven.price@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210416154309.22129-2-steven.price@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210427_104405_491208_1B96C2D4 X-CRM114-Status: GOOD ( 30.87 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Apr 16, 2021 at 04:43:04PM +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 which are !pte_valid_user() as these will > not have been swapped out. You should remove the pte_valid_user() mention from the commit log as well. > 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. 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). > mte_sync_tags(ptep, pte); > > __check_racy_pte_update(mm, ptep, pte); > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index b3c70a612c7a..e016ab57ea36 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -26,17 +26,23 @@ u64 gcr_kernel_excl __ro_after_init; > > static bool report_fault_once = true; > > -static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > +static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap, > + bool pte_is_tagged) > { > pte_t old_pte = READ_ONCE(*ptep); > > if (check_swap && is_swap_pte(old_pte)) { > swp_entry_t entry = pte_to_swp_entry(old_pte); > > - if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) > + if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) { > + set_bit(PG_mte_tagged, &page->flags); > return; > + } > } > > + if (!pte_is_tagged || test_and_set_bit(PG_mte_tagged, &page->flags)) > + return; I don't think we need another test_bit() here, it was done in the caller (bar potential races which need more thought). > + > page_kasan_tag_reset(page); > /* > * We need smp_wmb() in between setting the flags and clearing the > @@ -54,11 +60,13 @@ void mte_sync_tags(pte_t *ptep, pte_t pte) > struct page *page = pte_page(pte); > long i, nr_pages = compound_nr(page); > bool check_swap = nr_pages == 1; > + bool pte_is_tagged = pte_tagged(pte); > > /* if PG_mte_tagged is set, tags have already been initialised */ > for (i = 0; i < nr_pages; i++, page++) { > - if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > - mte_sync_page_tags(page, ptep, check_swap); > + if (!test_bit(PG_mte_tagged, &page->flags)) > + mte_sync_page_tags(page, ptep, check_swap, > + pte_is_tagged); > } > } You were right in the previous thread that if we have a race, it's already there even without your patches KVM patches. If it's the same pte in a multithreaded app, we should be ok as the core code holds the ptl (the arch code also holds the mmap_lock during exception handling but only as a reader, so you can have multiple holders). If there are multiple ptes to the same page, for example mapped with MAP_ANONYMOUS | MAP_SHARED, metadata recovery is done via arch_swap_restore() before we even set the pte and with the page locked. So calling lock_page() again in mte_restore_tags() would deadlock. I can see that do_swap_page() also holds the page lock around set_pte_at(), so I think we are covered. Any other scenario I may have missed? My understanding is that if the pte is the same, we have the ptl. Otherwise we have the page lock for shared pages. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel