From patchwork Fri Apr 19 07:43:40 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ryan Roberts X-Patchwork-Id: 13635733 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 9579FC15D; Fri, 19 Apr 2024 07:44:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713512646; cv=none; b=TyiGBcfXeD84R7GlaaTeVVYkW6m0upB9NwoadIRaNIufW5pYadC1X0WAH+37WHT030HitPyxtaG34LVNu5uk4C7QqODNWI8ja1cQyjm1XqoMDJZGTYneJ14qgVtNITJSiZ1KT1/JgAF038XasHdVEnTVDefskgmL7UnWPMT/Wv8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713512646; c=relaxed/simple; bh=hAY0+3UrRpRD+oKDHhysTAMhrmtmVoJ4mxOOyBbhG0g=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Iee6kPKZsVGbHzBKFX8rcW5yXww4IkEnYelJhEnb3w9teaJfww92ZGR7/ZXTvf45FYaDd/VyDQ0fGQCR26vjSGjyb9ppx1LiPagRSmf0NhTQ6hFg1JtOwxZdEA83FfEd/PxHxJo/wI3GLpTAHTGuuVXdYUJvp19oW4lNx5XK+NA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5C18F339; Fri, 19 Apr 2024 00:44:26 -0700 (PDT) Received: from e125769.cambridge.arm.com (e125769.cambridge.arm.com [10.1.196.27]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0D9543F792; Fri, 19 Apr 2024 00:43:55 -0700 (PDT) From: Ryan Roberts To: Catalin Marinas , Will Deacon , Andrew Morton , Shuah Khan , Joey Gouly , Ard Biesheuvel , Mark Rutland , Anshuman Khandual , David Hildenbrand , Shivansh Vij Cc: Ryan Roberts , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: [PATCH v1 1/5] arm64/mm: Move PTE_PROT_NONE and PMD_PRESENT_INVALID Date: Fri, 19 Apr 2024 08:43:40 +0100 Message-Id: <20240419074344.2643212-2-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20240419074344.2643212-1-ryan.roberts@arm.com> References: <20240419074344.2643212-1-ryan.roberts@arm.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Previously PTE_PROT_NONE was occupying bit 58, one of the bits reserved for SW use when the PTE is valid. This is a waste of those precious SW bits since PTE_PROT_NONE can only ever be set when valid is clear. Instead let's overlay it on what would be a HW bit if valid was set. We need to be careful about which HW bit to choose since some of them must be preserved; when pte_present() is true (as it is for a PTE_PROT_NONE pte), it is legitimate for the core to call various accessors, e.g. pte_dirty(), pte_write() etc. There are also some accessors that are private to the arch which must continue to be honoured, e.g. pte_user(), pte_user_exec() etc. So we choose to overlay PTE_UXN; This effectively means that whenever a pte has PTE_PROT_NONE set, it will always report pte_user_exec() == false, which is obviously always correct. As a result of this change, we must shuffle the layout of the arch-specific swap pte so that PTE_PROT_NONE is always zero and not overlapping with any other field. As a result of this, there is no way to keep the `type` field contiguous without conflicting with PMD_PRESENT_INVALID (bit 59), which must also be 0 for a swap pte. So let's move PMD_PRESENT_INVALID to bit 60. In the end, this frees up bit 58 for future use as a proper SW bit (e.g. soft-dirty or uffd-wp). Signed-off-by: Ryan Roberts --- arch/arm64/include/asm/pgtable-prot.h | 4 ++-- arch/arm64/include/asm/pgtable.h | 16 +++++++++------- 2 files changed, 11 insertions(+), 9 deletions(-) -- 2.25.1 diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h index dd9ee67d1d87..ef952d69fd04 100644 --- a/arch/arm64/include/asm/pgtable-prot.h +++ b/arch/arm64/include/asm/pgtable-prot.h @@ -18,14 +18,14 @@ #define PTE_DIRTY (_AT(pteval_t, 1) << 55) #define PTE_SPECIAL (_AT(pteval_t, 1) << 56) #define PTE_DEVMAP (_AT(pteval_t, 1) << 57) -#define PTE_PROT_NONE (_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */ +#define PTE_PROT_NONE (PTE_UXN) /* Reuse PTE_UXN; only when !PTE_VALID */ /* * This bit indicates that the entry is present i.e. pmd_page() * still points to a valid huge page in memory even if the pmd * has been invalidated. */ -#define PMD_PRESENT_INVALID (_AT(pteval_t, 1) << 59) /* only when !PMD_SECT_VALID */ +#define PMD_PRESENT_INVALID (_AT(pteval_t, 1) << 60) /* only when !PMD_SECT_VALID */ #define _PROT_DEFAULT (PTE_TYPE_PAGE | PTE_AF | PTE_SHARED) #define _PROT_SECT_DEFAULT (PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index afdd56d26ad7..23aabff4fa6f 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -1248,20 +1248,22 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma, * Encode and decode a swap entry: * bits 0-1: present (must be zero) * bits 2: remember PG_anon_exclusive - * bits 3-7: swap type - * bits 8-57: swap offset - * bit 58: PTE_PROT_NONE (must be zero) + * bits 4-53: swap offset + * bit 54: PTE_PROT_NONE (overlays PTE_UXN) (must be zero) + * bits 55-59: swap type + * bit 60: PMD_PRESENT_INVALID (must be zero) */ -#define __SWP_TYPE_SHIFT 3 +#define __SWP_TYPE_SHIFT 55 #define __SWP_TYPE_BITS 5 -#define __SWP_OFFSET_BITS 50 #define __SWP_TYPE_MASK ((1 << __SWP_TYPE_BITS) - 1) -#define __SWP_OFFSET_SHIFT (__SWP_TYPE_BITS + __SWP_TYPE_SHIFT) +#define __SWP_OFFSET_SHIFT 4 +#define __SWP_OFFSET_BITS 50 #define __SWP_OFFSET_MASK ((1UL << __SWP_OFFSET_BITS) - 1) #define __swp_type(x) (((x).val >> __SWP_TYPE_SHIFT) & __SWP_TYPE_MASK) #define __swp_offset(x) (((x).val >> __SWP_OFFSET_SHIFT) & __SWP_OFFSET_MASK) -#define __swp_entry(type,offset) ((swp_entry_t) { ((type) << __SWP_TYPE_SHIFT) | ((offset) << __SWP_OFFSET_SHIFT) }) +#define __swp_entry(type, offset) ((swp_entry_t) { ((unsigned long)(type) << __SWP_TYPE_SHIFT) | \ + ((unsigned long)(offset) << __SWP_OFFSET_SHIFT) }) #define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) }) #define __swp_entry_to_pte(swp) ((pte_t) { (swp).val })