From patchwork Tue Jul 5 14:26:19 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Catalin Marinas X-Patchwork-Id: 12906639 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 54907C433EF for ; Tue, 5 Jul 2022 14:28:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=nAK+ZADfxXrr9ujRW086Xi8fJb0k4iaTy6M4fuhwowI=; b=1hxR+R6128yMLZ /Fd/BlvqqWjWG9o1Pl5Hos/JLZuKgm198rJsb73/gS2c9oWCfMyLpuc5z87NqnwVKtC2lack7umi0 JMDSK/pHW2J90wMUYA5RpzG0rYrc6lxZShXLOOmM5ngqcUweYpVJt7P4vfYXANqlaWqUZCdhhwtHE B4izagGU/CFzTQppkQ2q5kDldTMi+/ZRGLFoypQmCdy8aMOObXubPt/lNXIy3uNTQkCvAiOR9oa8g +9syAjx1egr5YkwEEy5l7VlAstTigtgKG14mZonx1mwQVhBfxflYvURbCpPDa9zn2DtdswXJJ6nZC OPkoBOQymO5RG6hHe+Jw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1o8jW6-000nyU-8l; Tue, 05 Jul 2022 14:27:06 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1o8jVX-000nna-Mm for linux-arm-kernel@lists.infradead.org; Tue, 05 Jul 2022 14:26:34 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 2B9216198B; Tue, 5 Jul 2022 14:26:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2C3CAC341CF; Tue, 5 Jul 2022 14:26:29 +0000 (UTC) From: Catalin Marinas To: Will Deacon , Marc Zyngier , Steven Price , Peter Collingbourne Cc: Vincenzo Frascino , linux-arm-kernel@lists.infradead.org Subject: [PATCH 4/4] arm64: mte: Lock a page for MTE tag initialisation Date: Tue, 5 Jul 2022 15:26:19 +0100 Message-Id: <20220705142619.4135905-5-catalin.marinas@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220705142619.4135905-1-catalin.marinas@arm.com> References: <20220705142619.4135905-1-catalin.marinas@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220705_072631_878470_53077700 X-CRM114-Status: GOOD ( 27.95 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Initialising the tags and setting PG_mte_tagged flag for a page can race between multiple set_pte_at() on shared pages or setting the stage 2 pte via user_mem_abort(). Introduce a new PG_mte_lock flag as PG_arch_3 and set it before attempting page initialisation. Given that PG_mte_tagged is never cleared for a page, consider setting this flag to mean page unlocked and wait on this bit with acquire semantics if the page is locked: - try_page_mte_tagging() - lock the page for tagging, return true if it can be tagged, false if already tagged. No acquire semantics if it returns true (PG_mte_tagged not set) as there is no serialisation with a previous set_page_mte_tagged(). - set_page_mte_tagged() - set PG_mte_tagged with release semantics. The two-bit locking is based on Peter Colingbourne's idea. Signed-off-by: Catalin Marinas Cc: Will Deacon Cc: Marc Zyngier Cc: Steven Price Cc: Peter Collingbourne --- arch/arm64/include/asm/mte.h | 32 ++++++++++++++++++++++++++++++++ arch/arm64/include/asm/pgtable.h | 1 + arch/arm64/kernel/cpufeature.c | 2 +- arch/arm64/kernel/mte.c | 7 +++++-- arch/arm64/kvm/guest.c | 16 ++++++++++------ arch/arm64/kvm/mmu.c | 2 +- arch/arm64/mm/copypage.c | 2 ++ arch/arm64/mm/fault.c | 2 ++ arch/arm64/mm/mteswap.c | 3 +++ 9 files changed, 57 insertions(+), 10 deletions(-) diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h index c69218c56980..29712fc9df8c 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h @@ -36,6 +36,8 @@ void mte_free_tag_storage(char *storage); /* track which pages have valid allocation tags */ #define PG_mte_tagged PG_arch_2 +/* simple lock to avoid multiple threads tagging the same page */ +#define PG_mte_lock PG_arch_3 static inline void set_page_mte_tagged(struct page *page) { @@ -60,6 +62,32 @@ static inline bool page_mte_tagged(struct page *page) return ret; } +/* + * Lock the page for tagging and return 'true' if the page can be tagged, + * 'false' if already tagged. PG_mte_tagged is never cleared and therefore the + * locking only happens once for page initialisation. + * + * The page MTE lock state: + * + * Locked: PG_mte_lock && !PG_mte_tagged + * Unlocked: !PG_mte_lock || PG_mte_tagged + * + * Acquire semantics only if the page is tagged (returning 'false'). + */ +static inline bool try_page_mte_tagging(struct page *page) +{ + if (!test_and_set_bit(PG_mte_lock, &page->flags)) + return !page_mte_tagged(page); + + /* + * The tags are being initialised, wait for the PG_mte_tagged flag to + * be set. + */ + smp_cond_load_acquire(&page->flags, VAL & (1UL << PG_mte_tagged)); + + return false; +} + void mte_zero_clear_page_tags(void *addr); void mte_sync_tags(pte_t old_pte, pte_t pte); void mte_copy_page_tags(void *kto, const void *kfrom); @@ -84,6 +112,10 @@ static inline bool page_mte_tagged(struct page *page) { return false; } +static inline bool try_page_mte_tagging(struct page *page) +{ + return false; +} static inline void mte_zero_clear_page_tags(void *addr) { } diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 08823669db0a..ce2dc72f64f4 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -1033,6 +1033,7 @@ static inline void arch_swap_invalidate_area(int type) #define __HAVE_ARCH_SWAP_RESTORE static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio) { + /* mte_restore_tags() takes the PG_mte_lock */ if (system_supports_mte() && mte_restore_tags(entry, &folio->page)) set_page_mte_tagged(&folio->page); } diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 4478e5774580..c07dd7916517 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1964,7 +1964,7 @@ static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap) * Clear the tags in the zero page. This needs to be done via the * linear map which has the Tagged attribute. */ - if (!page_mte_tagged(ZERO_PAGE(0))) { + if (try_page_mte_tagging(ZERO_PAGE(0))) { mte_clear_page_tags(lm_alias(empty_zero_page)); set_page_mte_tagged(ZERO_PAGE(0)); } diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index 67e82ce4c285..54d284a1e0a7 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -41,6 +41,7 @@ static void mte_sync_page_tags(struct page *page, pte_t old_pte, if (check_swap && is_swap_pte(old_pte)) { swp_entry_t entry = pte_to_swp_entry(old_pte); + /* mte_restore_tags() takes the PG_mte_lock */ if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) { set_page_mte_tagged(page); return; @@ -59,8 +60,10 @@ static void mte_sync_page_tags(struct page *page, pte_t old_pte, * the new page->flags are visible before the tags were updated. */ smp_wmb(); - mte_clear_page_tags(page_address(page)); - set_page_mte_tagged(page); + if (try_page_mte_tagging(page)) { + mte_clear_page_tags(page_address(page)); + set_page_mte_tagged(page); + } } void mte_sync_tags(pte_t old_pte, pte_t pte) diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c index 3b04e69006b4..059b38e7a9e8 100644 --- a/arch/arm64/kvm/guest.c +++ b/arch/arm64/kvm/guest.c @@ -1067,15 +1067,19 @@ long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, clear_user(tags, MTE_GRANULES_PER_PAGE); kvm_release_pfn_clean(pfn); } else { + /* + * Only locking to serialise with a concurrent + * set_pte_at() in the VMM but still overriding the + * tags, hence ignoring the return value. + */ + try_page_mte_tagging(page); num_tags = mte_copy_tags_from_user(maddr, tags, MTE_GRANULES_PER_PAGE); - /* - * Set the flag after checking the write - * completed fully - */ - if (num_tags == MTE_GRANULES_PER_PAGE) - set_page_mte_tagged(page); + /* uaccess failed, don't leave stale tags */ + if (num_tags != MTE_GRANULES_PER_PAGE) + mte_clear_page_tags(page); + set_page_mte_tagged(page); kvm_release_pfn_dirty(pfn); } diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 35850f17ae08..fdd46089f260 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1066,7 +1066,7 @@ static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn, return; for (i = 0; i < nr_pages; i++, page++) { - if (!page_mte_tagged(page)) { + if (try_page_mte_tagging(page)) { mte_clear_page_tags(page_address(page)); set_page_mte_tagged(page); } diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c index f36d796f1bce..9c73bc020894 100644 --- a/arch/arm64/mm/copypage.c +++ b/arch/arm64/mm/copypage.c @@ -31,6 +31,8 @@ void copy_highpage(struct page *to, struct page *from) * the new page->flags are visible before the tags were updated. */ smp_wmb(); + /* It's a new page, shouldn't have been tagged yet */ + WARN_ON_ONCE(!try_page_mte_tagging(to)); mte_copy_page_tags(kto, kfrom); set_page_mte_tagged(to); } diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 147fe28d3fbe..bd28d6bd9286 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -926,6 +926,8 @@ struct page *alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma, void tag_clear_highpage(struct page *page) { + /* Newly allocated page, shouldn't have been tagged yet */ + WARN_ON_ONCE(!try_page_mte_tagging(page)); mte_zero_clear_page_tags(page_address(page)); page_kasan_tag_reset(page); set_page_mte_tagged(page); diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c index 9d3a8cf388fc..aec76a4423e9 100644 --- a/arch/arm64/mm/mteswap.c +++ b/arch/arm64/mm/mteswap.c @@ -62,6 +62,9 @@ bool mte_restore_tags(swp_entry_t entry, struct page *page) * the new page->flags are visible before the tags were updated. */ smp_wmb(); + /* racing tag restoring? */ + if (!try_page_mte_tagging(page)) + return false; mte_restore_page_tags(page_address(page), tags); return true;