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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 032FEC43334 for ; Fri, 22 Jul 2022 01:51:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229441AbiGVBvI (ORCPT ); Thu, 21 Jul 2022 21:51:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233463AbiGVBvH (ORCPT ); Thu, 21 Jul 2022 21:51:07 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1088991CD3 for ; Thu, 21 Jul 2022 18:51:06 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id z6-20020a056902054600b00670e3c8b43fso441510ybs.23 for ; Thu, 21 Jul 2022 18:51:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=k9HnMXUCeuGDqS8b473pt3twSYHG3RwHkZdL85ZMiGU=; b=HVnCwooJnMCJZaj1v28UbTZmc/ntcmSfrVpH4yB42SA6KpjbhZnQvjtzu+WCHB+hK8 wJqnUKi0TMmWLxQeb3gpqKS3SIohINGpFvz+6AmscMlFpsAIYX1Szk5kS85vIwm4cUHv 8aNxmmZgpAMS/0UxoANDB2ZrYiGxwf/r0d9zmkr2eF8AHX55KNimrfVqu/hkgjA4likh LdsMc0xUXWqK9gNfbtEpWr8UOpxtDvSO8vfrDCjIdzWDIKArkcdnVFcTYfvwYVqzxOcS bL3dCym6ThEzJP0A3L6HHVMWfcgmXPfMKSK88u/WvQykF43FkLzBwo83oQLrPto1mvD+ cH7g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=k9HnMXUCeuGDqS8b473pt3twSYHG3RwHkZdL85ZMiGU=; b=yFfVVEQmrPhcqQmGFOwI9tQGdJkYdeIZbfFNwf9O7tHhARCHC9VCtJ+jclmTuFXqZ4 MkjTnEhVnY6sLk9X9CHYNsZnGSG746cJRjHjzsIIfuZoqMgd2Ce8IPF4j3oAH+Ma7kH1 3aoBu7hfIkHtwaBU9In4VPbBjEDHfEBHdypv7FHkpFBRzJBYJkhojHzeozPMU6m9XzpW VM0rmN5DsTRStJKMZYVfx7Mv9Te6uZ3iyITAu75JNK6G9IbOXZZl+wo56X1DaFG2DM4w eydkTq8uxLDn5VCEkeq5VBQRDpezddm/ZFt0RKPtE1o4PxqH3SyRv7wZLOztfKigh5F6 S+4g== X-Gm-Message-State: AJIora+TiYHGkItqk5u4ubiW8rvg++3tQp62/fSDbxY2vvwR2EUOrrx5 12qDojNTfpo2dWqXMcpZuY5gxMk= X-Google-Smtp-Source: AGRyM1vMbAJ8s+S/tbABFbKabj9wTHVONvg7aMOuknXjfNhi2d/JpNFiqLLN/3A3eiaufTAkbLR2wGQ= X-Received: from pcc-desktop.svl.corp.google.com ([2620:15c:2ce:200:7ed4:5864:d5e1:ffe1]) (user=pcc job=sendgmr) by 2002:a5b:44d:0:b0:66f:ad5a:9d0b with SMTP id s13-20020a5b044d000000b0066fad5a9d0bmr1185324ybp.79.1658454665263; Thu, 21 Jul 2022 18:51:05 -0700 (PDT) Date: Thu, 21 Jul 2022 18:50:30 -0700 In-Reply-To: <20220722015034.809663-1-pcc@google.com> Message-Id: <20220722015034.809663-5-pcc@google.com> Mime-Version: 1.0 References: <20220722015034.809663-1-pcc@google.com> X-Mailer: git-send-email 2.37.1.359.gd136c6c3e2-goog Subject: [PATCH v2 4/7] arm64: mte: Lock a page for MTE tag initialisation From: Peter Collingbourne To: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu Cc: Catalin Marinas , Cornelia Huck , Will Deacon , Marc Zyngier , Evgenii Stepanov , kvm@vger.kernel.org, Steven Price , Vincenzo Frascino , Peter Collingbourne Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: Catalin Marinas 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 Collingbourne'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..8e007046bba6 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 true; + + /* + * The tags are either being initialised or have already been 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 82719fa42c0e..e6b82ad1e9e6 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -1049,6 +1049,7 @@ 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 c66f0ffaaf47..31787dafe95e 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -2020,7 +2020,7 @@ 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 2287316639f3..634e089b5933 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; @@ -50,8 +51,10 @@ static void mte_sync_page_tags(struct page *page, pte_t old_pte, if (!pte_is_tagged) return; - 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 1a3707aeb41f..750a69a97994 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 4223389b6180..a3fa650ceca4 100644 --- a/arch/arm64/mm/copypage.c +++ b/arch/arm64/mm/copypage.c @@ -22,6 +22,8 @@ void copy_highpage(struct page *to, struct page *from) copy_page(kto, kfrom); if (system_supports_mte() && page_mte_tagged(from)) { + /* 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 d095bfa16771..6407a29cab0d 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -930,6 +930,8 @@ 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)); set_page_mte_tagged(page); } diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c index a78c1db23c68..cd5ad0936e16 100644 --- a/arch/arm64/mm/mteswap.c +++ b/arch/arm64/mm/mteswap.c @@ -53,6 +53,9 @@ bool mte_restore_tags(swp_entry_t entry, struct page *page) if (!tags) return false; + /* racing tag restoring? */ + if (!try_page_mte_tagging(page)) + return false; mte_restore_page_tags(page_address(page), tags); return true; -- 2.37.1.359.gd136c6c3e2-goog