From nobody Sun Dec 28 02:45:01 2025 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 9847AC41535 for ; Thu, 14 Dec 2023 11:07:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1443997AbjLNLHS (ORCPT ); Thu, 14 Dec 2023 06:07:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42766 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1443948AbjLNLHE (ORCPT ); Thu, 14 Dec 2023 06:07:04 -0500 Received: from mail-yw1-x114a.google.com (mail-yw1-x114a.google.com [IPv6:2607:f8b0:4864:20::114a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E6DA5181 for ; Thu, 14 Dec 2023 03:06:57 -0800 (PST) Received: by mail-yw1-x114a.google.com with SMTP id 00721157ae682-5caf86963ecso89074657b3.3 for ; Thu, 14 Dec 2023 03:06:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1702552017; x=1703156817; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=ZQcjn3HKRIFjRjPtUqZGi0kpXnoJ+H0gJj/u7XtaxV0=; b=TIV8rAoiEI4nk710mLSezMYIcGA+Ny583BCnVwZxn+qAicCI5d1zUgt8tXhf3PO4Nn 6zSTt1jZshagzTIVMAZSWvXRujhPUMLjV65CNp9qc8n0FjkCcWRg589GUuB1PY5QSrVB GOCa/PBO6fMjC7GfNnbiHSMolSYNegA2jgK2wcrP7zaMB1nkz3+qpPYHkYnG3Z85qWzu XUHHu1euwkLoawERiZWWfL1S9dHe4Wubj1lXJQMGhj/DMOror0m4n2I+Mmaj2AnGWDtI pR+IQBGzxCk3L+KwnzP6nSISZXLQI04So6jmMqKXUYxW99Zcd5Gn6D5/0Jta4ouxpAMs xjpA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1702552017; x=1703156817; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=ZQcjn3HKRIFjRjPtUqZGi0kpXnoJ+H0gJj/u7XtaxV0=; b=MSybbsD9lnaOfHZoY8XfROK/59vrZ3xpMz8N0gpRDyJ3SAxEpsAFGaxURPMC8enemT Afl/fyQhaeDIC18BikuWVWzWXQmpBzQIFZNiYn8zhCXsBgJpBsTFcHWALimat1S+G2+d XBN3eptJdXJz36thLAs18P2jbMOQ81LYJUfP7+9psf+DJEKsRYOA/gCVnGB/DkJp17ww eg21pCZVw1P+LYF+X2lEszrLlX3MF5EdiiZh51w1cpWo+nnNPhSpL4se6rf6yKKkrrCO 8ADMsbzfCjgfWIVq2Ja/hi8LfyrPovYQ0TzfEbVAd28c5yYktrCDsbrbtXYwoG6lqhLc vCcg== X-Gm-Message-State: AOJu0YyYP8eqyJ70uTzwuPsPQw5ZgqIGN25W2eqPfedikCNIOkYpi/hg zyTc02JPxvivEZv/6dtFGgJ2nObifNk= X-Google-Smtp-Source: AGHT+IHZUxlk2ydWjkVM3eEnz5UgSsZtEHF9ttwaUfzN+X+521ZJ4sG4g8taV4ZW5sGtfxhkEsk7VUFm2Qs= X-Received: from glider.muc.corp.google.com ([2a00:79e0:9c:201:8447:3e89:1f77:ff8a]) (user=glider job=sendgmr) by 2002:a05:690c:a81:b0:5df:4a9b:fb6c with SMTP id ci1-20020a05690c0a8100b005df4a9bfb6cmr109547ywb.3.1702552017196; Thu, 14 Dec 2023 03:06:57 -0800 (PST) Date: Thu, 14 Dec 2023 12:06:36 +0100 In-Reply-To: <20231214110639.2294687-1-glider@google.com> Mime-Version: 1.0 References: <20231214110639.2294687-1-glider@google.com> X-Mailer: git-send-email 2.43.0.472.g3155946c3a-goog Message-ID: <20231214110639.2294687-5-glider@google.com> Subject: [PATCH v10-mte 4/7] arm64: mte: implement CONFIG_ARM64_MTE_COMP From: Alexander Potapenko To: glider@google.com, catalin.marinas@arm.com, will@kernel.org, pcc@google.com, andreyknvl@gmail.com, andriy.shevchenko@linux.intel.com, aleksander.lobakin@intel.com, linux@rasmusvillemoes.dk, yury.norov@gmail.com, alexandru.elisei@arm.com Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, eugenis@google.com, syednwaris@gmail.com, william.gray@linaro.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The config implements the algorithm compressing memory tags for ARM MTE during swapping. The algorithm is based on RLE and specifically targets buffers of tags corresponding to a single page. In many cases a buffer can be compressed into 63 bits, making it possible to store it without additional memory allocation. Suggested-by: Evgenii Stepanov Signed-off-by: Alexander Potapenko Acked-by: Catalin Marinas --- v10-mte: - added Catalin's Acked-by: v8: - As suggested by Catalin Marinas, only compress tags if they can be stored inline. This simplifies the code drastically. - Update the documentation. - Split off patches introducing bitmap_read()/bitmap_write(). v6: - shuffle bits in inline handles so that they can't be confused with canonical pointers; - use kmem_cache_zalloc() to allocate compressed storage - correctly handle range size overflow - minor documentation fixes, clarify the special cases v5: - make code PAGE_SIZE-agnostic, remove hardcoded constants, updated the docs - implement debugfs interface - Address comments by Andy Shevchenko: - update description of mtecomp.c - remove redundant assignments, simplify mte_tags_to_ranges() - various code simplifications - introduce mtecomp.h - add :export: to Documentation/arch/arm64/mte-tag-compression.rst v4: - Addressed comments by Andy Shevchenko: - expanded "MTE" to "Memory Tagging Extension" in Kconfig - fixed kernel-doc comments, moved them to C source - changed variables to unsigned where applicable - some code simplifications, fewer unnecessary assignments - added the mte_largest_idx_bits() helper - added namespace prefixes to all functions - added missing headers (but removed bits.h) - Addressed comments by Yury Norov: - removed test-only functions from mtecomp.h - dropped the algoritm name (all functions are now prefixed with "mte") - added more comments - got rid of MTE_RANGES_INLINE - renamed bitmap_{get,set}_value() to bitmap_{read,write}() - moved the big comment explaining the algorithm to Documentation/arch/arm64/mte-tag-compression.rst, expanded it, add a link to it from Documentation/arch/arm64/index.rst - removed hardcoded ranges from mte_alloc_size()/mte_size_to_ranges() v3: - Addressed comments by Andy Shevchenko: - use bitmap_{set,get}_value() writte by Syed Nayyar Waris - switched to unsigned long everywhere (fewer casts) - simplified the code, removed redundant checks - dropped ea0_compress_inline() - added bit size constants and helpers to access the bitmap - explicitly initialize all compressed sizes in ea0_compress_to_buf() - initialize all handle bits v2: - as suggested by Yury Norov, switched from struct bitq (which is not needed anymore) to - add missing symbol exports --- Documentation/arch/arm64/index.rst | 1 + .../arch/arm64/mte-tag-compression.rst | 154 +++++++++++ arch/arm64/Kconfig | 11 + arch/arm64/include/asm/mtecomp.h | 39 +++ arch/arm64/mm/Makefile | 1 + arch/arm64/mm/mtecomp.c | 257 ++++++++++++++++++ arch/arm64/mm/mtecomp.h | 12 + 7 files changed, 475 insertions(+) create mode 100644 Documentation/arch/arm64/mte-tag-compression.rst create mode 100644 arch/arm64/include/asm/mtecomp.h create mode 100644 arch/arm64/mm/mtecomp.c create mode 100644 arch/arm64/mm/mtecomp.h diff --git a/Documentation/arch/arm64/index.rst b/Documentation/arch/arm64/= index.rst index d08e924204bf1..bf6c1583233a9 100644 --- a/Documentation/arch/arm64/index.rst +++ b/Documentation/arch/arm64/index.rst @@ -19,6 +19,7 @@ ARM64 Architecture legacy_instructions memory memory-tagging-extension + mte-tag-compression perf pointer-authentication ptdump diff --git a/Documentation/arch/arm64/mte-tag-compression.rst b/Documentati= on/arch/arm64/mte-tag-compression.rst new file mode 100644 index 0000000000000..8fe6b51a9db6d --- /dev/null +++ b/Documentation/arch/arm64/mte-tag-compression.rst @@ -0,0 +1,154 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D +Tag Compression for Memory Tagging Extension (MTE) +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D + +This document describes the algorithm used to compress memory tags used by= the +ARM Memory Tagging Extension (MTE). + +Introduction +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +MTE assigns tags to memory pages: for 4K pages those tags occupy 128 bytes +(256 4-bit tags each corresponding to a 16-byte MTE granule), for 16K page= s - +512 bytes, for 64K pages - 2048 bytes. By default, MTE carves out 3.125% (= 1/16) +of the available physical memory to store the tags. + +When MTE pages are saved to swap, their tags need to be stored in the kern= el +memory. If the system swap is used heavily, these tags may take a substant= ial +portion of the physical memory. To reduce memory waste, ``CONFIG_ARM64_MTE= _COMP`` +allows the kernel to store the tags in compressed form. + +Implementation details +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +The algorithm attempts to compress an array of ``MTE_PAGE_TAG_STORAGE`` +tag bytes into a byte sequence that can be stored in an 8-byte pointer. If= that +is not possible, the data is stored uncompressed. + +Tag manipulation and storage +---------------------------- + +Tags for swapped pages are stored in an XArray that maps swap entries to 6= 3-bit +values (see ``arch/arm64/mm/mteswap.c``). Bit 0 of these values indicates = how +their contents should be treated: + + - 0: value is a pointer to an uncompressed buffer allocated with kmalloc() + (always the case if ``CONFIG_ARM64_MTE_COMP=3Dn``) with the highest bit= set + to 0; + - 1: value contains compressed data. + +``arch/arm64/include/asm/mtecomp.h`` declares the following functions that +manipulate with tags: + +- mte_compress() - compresses the given ``MTE_PAGE_TAG_STORAGE``-byte ``ta= gs`` + buffer into a pointer; +- mte_decompress() - decompresses the tags from a pointer; +- mte_is_compressed() - returns ``true`` iff the pointer passed to it shou= ld be + treated as compressed data. + +Tag compression +--------------- + +The compression algorithm is a variation of RLE (run-length encoding) and = works +as follows (we will be considering 4K pages and 128-byte tag buffers, but = the +same approach scales to 16K and 64K pages): + +1. The input array of 128 (``MTE_PAGE_TAG_STORAGE``) bytes is transformed = into + tag ranges (two arrays: ``r_tags[]`` containing tag values and ``r_size= s[]`` + containing range lengths) by mte_tags_to_ranges(). Note that + ``r_sizes[]`` sums up to 256 (``MTE_GRANULES_PER_PAGE``). + + If ``r_sizes[]`` consists of a single element + (``{ MTE_GRANULES_PER_PAGE }``), the corresponding range is split into = two + halves, i.e.:: + + r_sizes_new[2] =3D { MTE_GRANULES_PER_PAGE/2, MTE_GRANULES_PER_PAGE/2= }; + r_tags_new[2] =3D { r_tags[0], r_tags[0] }; + +2. The number of the largest element of ``r_sizes[]`` is stored in + ``largest_idx``. The element itself is thrown away from ``r_sizes[]``, + because it can be reconstructed from the sum of the remaining elements.= Note + that now none of the remaining ``r_sizes[]`` elements exceeds + ``MTE_GRANULES_PER_PAGE/2``. + +3. If the number ``N`` of ranges does not exceed ``6``, the ranges can be + compressed into 64 bits. This is done by storing the following values p= acked + into the pointer (``i`` means a ````-bit unsigned integer) + treated as a bitmap (see ``include/linux/bitmap.h``):: + + bit 0 : (always 1) : i1 + bits 1-3 : largest_idx : i3 + bits 4-27 : r_tags[0..5] : i4 x 6 + bits 28-62 : r_sizes[0..4] : i7 x 5 + bit 63 : (always 0) : i1 + + If N is less than 6, ``r_tags`` and ``r_sizes`` are padded up with zero + values. The unused bits in the pointer, including bit 63, are also set = to 0, + so the compressed data can be stored in XArray. + + Range size of ``MTE_GRANULES_PER_PAGE/2`` (at most one) does not fit in= to + i7 and will be written as 0. This case is handled separately by the + decompressing procedure. + +Tag decompression +----------------- + +The decompression algorithm performs the steps below. + +1. Read the lowest bit of the data from the input buffer and check that it= is 1, + otherwise bail out. + +2. Read ``largest_idx``, ``r_tags[]`` and ``r_sizes[]`` from the + input buffer. + + If ``largest_idx`` is zero, and all ``r_sizes[]`` are zero, set + ``r_sizes[0] =3D MTE_GRANULES_PER_PAGE/2``. + + Calculate the removed largest element of ``r_sizes[]`` as + ``largest =3D 256 - sum(r_sizes)`` and insert it into ``r_sizes`` at + position ``largest_idx``. + +6. For each ``r_sizes[i] > 0``, add a 4-bit value ``r_tags[i]`` to the out= put + buffer ``r_sizes[i]`` times. + + +Why these numbers? +------------------ + +To be able to reconstruct ``N`` tag ranges from the compressed data, we ne= ed to +store the indicator bit together with ``largest_idx``, ``r_tags[N]``, and +``r_sizes[N-1]`` in 63 bits. +Knowing that the sizes do not exceed ``MTE_PAGE_TAG_STORAGE``, each of the= m can be +packed into ``S =3D ilog2(MTE_PAGE_TAG_STORAGE)`` bits, whereas a single t= ag occupies +4 bits. + +It is evident that the number of ranges that can be stored in 63 bits is +strictly less than 8, therefore we only need 3 bits to store ``largest_idx= ``. + +The maximum values of ``N`` so that the number ``1 + 3 + N * 4 + (N-1) * S= `` of +storage bits does not exceed 63, are shown in the table below:: + + +-----------+-----------------+----+---+-------------------+ + | Page size | Tag buffer size | S | N | Storage bits | + +-----------+-----------------+----+---+-------------------+ + | 4 KB | 128 B | 7 | 6 | 63 =3D 1+3+6*4+5*7 | + | 16 KB | 512 B | 9 | 5 | 60 =3D 1+3+5*4+4*9 | + | 64 KB | 2048 B | 11 | 4 | 53 =3D 1+3+4*4+3*11 | + +-----------+-----------------+----+---+-------------------+ + +Note +---- + +Tag compression and decompression implicitly rely on the fixed MTE tag size +(4 bits) and number of tags per page. Should these values change, the algo= rithm +may need to be revised. + + +Programming Interface +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + + .. kernel-doc:: arch/arm64/include/asm/mtecomp.h + .. kernel-doc:: arch/arm64/mm/mtecomp.c + :export: diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 7b071a00425d2..5f4d4b49a512e 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -2078,6 +2078,17 @@ config ARM64_EPAN if the cpu does not implement the feature. endmenu # "ARMv8.7 architectural features" =20 +config ARM64_MTE_COMP + bool "Tag compression for ARM64 Memory Tagging Extension" + default y + depends on ARM64_MTE + help + Enable tag compression support for ARM64 Memory Tagging Extension. + + Tag buffers corresponding to swapped RAM pages are compressed using + RLE to conserve heap memory. In the common case compressed tags + occupy 2.5x less memory. + config ARM64_SVE bool "ARM Scalable Vector Extension support" default y diff --git a/arch/arm64/include/asm/mtecomp.h b/arch/arm64/include/asm/mtec= omp.h new file mode 100644 index 0000000000000..b9a3a921a38d4 --- /dev/null +++ b/arch/arm64/include/asm/mtecomp.h @@ -0,0 +1,39 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef __ASM_MTECOMP_H +#define __ASM_MTECOMP_H + +#include + +/** + * mte_is_compressed() - check if the supplied pointer contains compressed= tags. + * @ptr: pointer returned by kmalloc() or mte_compress(). + * + * Returns: true iff bit 0 of @ptr is 1, which is only possible if @ptr was + * returned by mte_is_compressed(). + */ +static inline bool mte_is_compressed(void *ptr) +{ + return ((unsigned long)ptr & 1); +} + +#if defined(CONFIG_ARM64_MTE_COMP) + +void *mte_compress(u8 *tags); +bool mte_decompress(void *handle, u8 *tags); + +#else + +static inline void *mte_compress(u8 *tags) +{ + return NULL; +} + +static inline bool mte_decompress(void *data, u8 *tags) +{ + return false; +} + +#endif // CONFIG_ARM64_MTE_COMP + +#endif // __ASM_MTECOMP_H diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile index dbd1bc95967d0..46778f6dd83c2 100644 --- a/arch/arm64/mm/Makefile +++ b/arch/arm64/mm/Makefile @@ -10,6 +10,7 @@ obj-$(CONFIG_TRANS_TABLE) +=3D trans_pgd.o obj-$(CONFIG_TRANS_TABLE) +=3D trans_pgd-asm.o obj-$(CONFIG_DEBUG_VIRTUAL) +=3D physaddr.o obj-$(CONFIG_ARM64_MTE) +=3D mteswap.o +obj-$(CONFIG_ARM64_MTE_COMP) +=3D mtecomp.o KASAN_SANITIZE_physaddr.o +=3D n =20 obj-$(CONFIG_KASAN) +=3D kasan_init.o diff --git a/arch/arm64/mm/mtecomp.c b/arch/arm64/mm/mtecomp.c new file mode 100644 index 0000000000000..c948921525030 --- /dev/null +++ b/arch/arm64/mm/mtecomp.c @@ -0,0 +1,257 @@ +// SPDX-License-Identifier: GPL-2.0-only + +/* + * MTE tag compression algorithm. + * See Documentation/arch/arm64/mte-tag-compression.rst for more details. + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include + +#include "mtecomp.h" + +#define MTE_BITS_PER_LARGEST_IDX 3 +/* Range size cannot exceed MTE_GRANULES_PER_PAGE / 2. */ +#define MTE_BITS_PER_SIZE (ilog2(MTE_GRANULES_PER_PAGE) - 1) + +/* + * See Documentation/arch/arm64/mte-tag-compression.rst for details on how= the + * maximum number of ranges is calculated. + */ +#if defined(CONFIG_ARM64_4K_PAGES) +#define MTE_MAX_RANGES 6 +#elif defined(CONFIG_ARM64_16K_PAGES) +#define MTE_MAX_RANGES 5 +#else +#define MTE_MAX_RANGES 4 +#endif + +/** + * mte_tags_to_ranges() - break @tags into arrays of tag ranges. + * @tags: MTE_GRANULES_PER_PAGE-byte array containing MTE tags. + * @out_tags: u8 array to store the tag of every range. + * @out_sizes: unsigned short array to store the size of every range. + * @out_len: length of @out_tags and @out_sizes (output parameter, initial= ly + * equal to lengths of out_tags[] and out_sizes[]). + * + * This function is exported for testing purposes. + */ +void mte_tags_to_ranges(u8 *tags, u8 *out_tags, unsigned short *out_sizes, + size_t *out_len) +{ + u8 prev_tag =3D tags[0] / 16; /* First tag in the array. */ + unsigned int cur_idx =3D 0, i, j; + u8 cur_tag; + + memset(out_tags, 0, array_size(*out_len, sizeof(*out_tags))); + memset(out_sizes, 0, array_size(*out_len, sizeof(*out_sizes))); + + out_tags[cur_idx] =3D prev_tag; + for (i =3D 0; i < MTE_GRANULES_PER_PAGE; i++) { + j =3D i % 2; + cur_tag =3D j ? (tags[i / 2] % 16) : (tags[i / 2] / 16); + if (cur_tag =3D=3D prev_tag) { + out_sizes[cur_idx]++; + } else { + cur_idx++; + prev_tag =3D cur_tag; + out_tags[cur_idx] =3D prev_tag; + out_sizes[cur_idx] =3D 1; + } + } + *out_len =3D cur_idx + 1; +} +EXPORT_SYMBOL_NS(mte_tags_to_ranges, MTECOMP); + +/** + * mte_ranges_to_tags() - fill @tags using given tag ranges. + * @r_tags: u8[] containing the tag of every range. + * @r_sizes: unsigned short[] containing the size of every range. + * @r_len: length of @r_tags and @r_sizes. + * @tags: MTE_GRANULES_PER_PAGE-byte array to write the tags to. + * + * This function is exported for testing purposes. + */ +void mte_ranges_to_tags(u8 *r_tags, unsigned short *r_sizes, size_t r_len, + u8 *tags) +{ + unsigned int i, j, pos =3D 0; + u8 prev; + + for (i =3D 0; i < r_len; i++) { + for (j =3D 0; j < r_sizes[i]; j++) { + if (pos % 2) + tags[pos / 2] =3D (prev << 4) | r_tags[i]; + else + prev =3D r_tags[i]; + pos++; + } + } +} +EXPORT_SYMBOL_NS(mte_ranges_to_tags, MTECOMP); + +static void mte_bitmap_write(unsigned long *bitmap, unsigned long value, + unsigned long *pos, unsigned long bits) +{ + bitmap_write(bitmap, value, *pos, bits); + *pos +=3D bits; +} + +/* Compress ranges into an unsigned long. */ +static void mte_compress_to_ulong(size_t len, u8 *tags, unsigned short *si= zes, + unsigned long *result) +{ + unsigned long bit_pos =3D 0; + unsigned int largest_idx, i; + unsigned short largest =3D 0; + + for (i =3D 0; i < len; i++) { + if (sizes[i] > largest) { + largest =3D sizes[i]; + largest_idx =3D i; + } + } + /* Bit 1 in position 0 indicates compressed data. */ + mte_bitmap_write(result, 1, &bit_pos, 1); + mte_bitmap_write(result, largest_idx, &bit_pos, + MTE_BITS_PER_LARGEST_IDX); + for (i =3D 0; i < len; i++) + mte_bitmap_write(result, tags[i], &bit_pos, MTE_TAG_SIZE); + if (len =3D=3D 1) { + /* + * We are compressing MTE_GRANULES_PER_PAGE of identical tags. + * Split it into two ranges containing + * MTE_GRANULES_PER_PAGE / 2 tags, so that it falls into the + * special case described below. + */ + mte_bitmap_write(result, tags[0], &bit_pos, MTE_TAG_SIZE); + i =3D 2; + } else { + i =3D len; + } + for (; i < MTE_MAX_RANGES; i++) + mte_bitmap_write(result, 0, &bit_pos, MTE_TAG_SIZE); + /* + * Most of the time sizes[i] fits into MTE_BITS_PER_SIZE, apart from a + * special case when: + * len =3D 2; + * sizes =3D { MTE_GRANULES_PER_PAGE / 2, MTE_GRANULES_PER_PAGE / 2}; + * In this case largest_idx will be set to 0, and the size written to + * the bitmap will be also 0. + */ + for (i =3D 0; i < len; i++) { + if (i !=3D largest_idx) + mte_bitmap_write(result, sizes[i], &bit_pos, + MTE_BITS_PER_SIZE); + } + for (i =3D len; i < MTE_MAX_RANGES; i++) + mte_bitmap_write(result, 0, &bit_pos, MTE_BITS_PER_SIZE); +} + +/** + * mte_compress() - compress the given tag array. + * @tags: MTE_GRANULES_PER_PAGE-byte array to read the tags from. + * + * Attempts to compress the user-supplied tag array. + * + * Returns: compressed data or NULL. + */ +void *mte_compress(u8 *tags) +{ + unsigned short *r_sizes; + void *result =3D NULL; + u8 *r_tags; + size_t r_len; + + r_sizes =3D kmalloc_array(MTE_GRANULES_PER_PAGE, sizeof(unsigned short), + GFP_KERNEL); + r_tags =3D kmalloc(MTE_GRANULES_PER_PAGE, GFP_KERNEL); + if (!r_sizes || !r_tags) + goto ret; + r_len =3D MTE_GRANULES_PER_PAGE; + mte_tags_to_ranges(tags, r_tags, r_sizes, &r_len); + if (r_len <=3D MTE_MAX_RANGES) + mte_compress_to_ulong(r_len, r_tags, r_sizes, + (unsigned long *)&result); +ret: + kfree(r_tags); + kfree(r_sizes); + return result; +} +EXPORT_SYMBOL_NS(mte_compress, MTECOMP); + +static unsigned long mte_bitmap_read(const unsigned long *bitmap, + unsigned long *pos, unsigned long bits) +{ + unsigned long start =3D *pos; + + *pos +=3D bits; + return bitmap_read(bitmap, start, bits); +} + +/** + * mte_decompress() - decompress the tag array from the given pointer. + * @data: pointer returned by @mte_compress() + * @tags: MTE_GRANULES_PER_PAGE-byte array to write the tags to. + * + * Reads the compressed data and writes it into the user-supplied tag arra= y. + * + * Returns: true on success, false if the passed data is uncompressed. + */ +bool mte_decompress(void *data, u8 *tags) +{ + unsigned short r_sizes[MTE_MAX_RANGES]; + u8 r_tags[MTE_MAX_RANGES]; + unsigned int largest_idx, i; + unsigned long bit_pos =3D 0; + unsigned long *bitmap; + unsigned short sum; + size_t max_ranges; + + if (!mte_is_compressed(data)) + return false; + + bitmap =3D (unsigned long *)&data; + max_ranges =3D MTE_MAX_RANGES; + /* Skip the leading bit indicating the inline case. */ + mte_bitmap_read(bitmap, &bit_pos, 1); + largest_idx =3D + mte_bitmap_read(bitmap, &bit_pos, MTE_BITS_PER_LARGEST_IDX); + if (largest_idx >=3D MTE_MAX_RANGES) + return false; + + for (i =3D 0; i < max_ranges; i++) + r_tags[i] =3D mte_bitmap_read(bitmap, &bit_pos, MTE_TAG_SIZE); + for (i =3D 0, sum =3D 0; i < max_ranges; i++) { + if (i =3D=3D largest_idx) + continue; + r_sizes[i] =3D + mte_bitmap_read(bitmap, &bit_pos, MTE_BITS_PER_SIZE); + /* + * Special case: tag array consists of two ranges of + * `MTE_GRANULES_PER_PAGE / 2` tags. + */ + if ((largest_idx =3D=3D 0) && (i =3D=3D 1) && (r_sizes[i] =3D=3D 0)) + r_sizes[i] =3D MTE_GRANULES_PER_PAGE / 2; + if (!r_sizes[i]) { + max_ranges =3D i; + break; + } + sum +=3D r_sizes[i]; + } + if (sum >=3D MTE_GRANULES_PER_PAGE) + return false; + r_sizes[largest_idx] =3D MTE_GRANULES_PER_PAGE - sum; + mte_ranges_to_tags(r_tags, r_sizes, max_ranges, tags); + return true; +} +EXPORT_SYMBOL_NS(mte_decompress, MTECOMP); diff --git a/arch/arm64/mm/mtecomp.h b/arch/arm64/mm/mtecomp.h new file mode 100644 index 0000000000000..b94cf0384f2af --- /dev/null +++ b/arch/arm64/mm/mtecomp.h @@ -0,0 +1,12 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef ARCH_ARM64_MM_MTECOMP_H_ +#define ARCH_ARM64_MM_MTECOMP_H_ + +/* Functions exported from mtecomp.c for test_mtecomp.c. */ +void mte_tags_to_ranges(u8 *tags, u8 *out_tags, unsigned short *out_sizes, + size_t *out_len); +void mte_ranges_to_tags(u8 *r_tags, unsigned short *r_sizes, size_t r_len, + u8 *tags); + +#endif // ARCH_ARM64_MM_TEST_MTECOMP_H_ --=20 2.43.0.472.g3155946c3a-goog