From nobody Fri Dec 19 07:17:17 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 52AD733FE10; Tue, 16 Dec 2025 23:06:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765926420; cv=none; b=R1UVruQhNWxslfTi8j0o1L8km+Z+u9Y0mkohSlM7TMpRVEnfEe1ij3JMYGSMvIi2WTCLwsymV4bZeNCTZuS9CRDMBEBe17kVNByzAvkWPOSnGChZGBvI7QiDLhokg3IyHF/GIOso6nP4yL+ElysssP8QIQN/CWdsDS2bxjTpRog= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765926420; c=relaxed/simple; bh=UIh2lBlsCpMPvtCjHLE12Rw0UIMIzrvaY3f6XYfUzQQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=taHZNG/3Ynauv7KivxcAcj7urPPLOg8hVhBT2XN0bXwEJsawTkbVWFkehV0V7OlDwG5Tvq/RTMO4xr4JaLtqBwX98hOOJ1SRT1ERU7eVdIV+z1dFKUN8/O1FgXZ35g/sKI0rRrP31ZeM6SRRHUZube2Vnv86rZiB8cwUU9JidWs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=i03WIikQ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="i03WIikQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3DA3DC19424; Tue, 16 Dec 2025 23:06:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1765926419; bh=UIh2lBlsCpMPvtCjHLE12Rw0UIMIzrvaY3f6XYfUzQQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=i03WIikQgmRlD91C0gqlY2p/Tg3h/5o2ssYupnVC10kBfnLD6lWIvtx9zPBwkwcnz 9i7apTc7QNkWlIkN9ieHntj+OPrf6ZIyxVbsImu14Ap64Q+tCXmj8UFGxuoMGXOt9v PALa2mFhVH/ibY58qRjZwClkvBuRswN/b1fqywDX23IkIXb0g0GDvoYj1HYvj2bLSA MZBvYvPYY2CbyD/JjZk8E8Bqqx3+FZWmrNTyzJeH4QHL0N9IRo1348XP9QnIL0nW9t 0SZxsy53/VwPKCnYDAdPWKTENd9saDsa5FfK2dVEPXndH3xmg4Vh8v0iT4X26GeKoU 4NiuR/RXHkstQ== From: Eric Biggers To: dm-devel@lists.linux.dev, Alasdair Kergon , Mike Snitzer , Mikulas Patocka , Benjamin Marzinski Cc: Sami Tolvanen , Eran Messeri , linux-kernel@vger.kernel.org, Eric Biggers Subject: [PATCH 2/7] dm-verity: make dm_verity_fec_io::bufs variable-length Date: Tue, 16 Dec 2025 15:06:09 -0800 Message-ID: <20251216230614.51779-3-ebiggers@kernel.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251216230614.51779-1-ebiggers@kernel.org> References: <20251216230614.51779-1-ebiggers@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When correcting a data block, the FEC code performs optimally when it has enough buffers to hold all the needed RS blocks. That number of buffers is '1 << (v->data_dev_block_bits - DM_VERITY_FEC_BUF_RS_BITS)'. However, since v->data_dev_block_bits isn't a compile-time constant, the code actually used PAGE_SHIFT instead. With the traditional PAGE_SIZE =3D=3D data_block_size =3D=3D 4096, this was fine. However, when PAGE_SIZE > data_block_size, this wastes space. E.g., with data_block_size =3D=3D 4096 && PAGE_SIZE =3D=3D 16384, struct dm_verity_fec_io is 9240 bytes, when in fact only 3096 bytes are needed. Fix this by making dm_verity_fec_io::bufs a variable-length array. This makes the macros DM_VERITY_FEC_BUF_MAX and fec_for_each_extra_buffer() no longer apply, so remove them. Also remove the related macro fec_for_each_prealloc_buffer(), since DM_VERITY_FEC_BUF_PREALLOC is fixed at 1 and was already assumed to be 1 (considering that mempool_alloc() shouldn't be called in a loop). Signed-off-by: Eric Biggers --- drivers/md/dm-verity-fec.c | 41 ++++++++++++++++++++------------------ drivers/md/dm-verity-fec.h | 14 ++++++++----- 2 files changed, 31 insertions(+), 24 deletions(-) diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c index bf533ffa7d56..7574e65c32ae 100644 --- a/drivers/md/dm-verity-fec.c +++ b/drivers/md/dm-verity-fec.c @@ -8,10 +8,22 @@ #include "dm-verity-fec.h" #include =20 #define DM_MSG_PREFIX "verity-fec" =20 +/* + * When correcting a data block, the FEC code performs optimally when it c= an + * collect all the associated RS blocks at the same time. As each byte is= part + * of a different RS block, there are '1 << data_dev_block_bits' RS blocks. + * There are '1 << DM_VERITY_FEC_BUF_RS_BITS' RS blocks per buffer, so that + * gives '1 << (data_dev_block_bits - DM_VERITY_FEC_BUF_RS_BITS)' buffers. + */ +static inline unsigned int fec_max_nbufs(struct dm_verity *v) +{ + return 1 << (v->data_dev_block_bits - DM_VERITY_FEC_BUF_RS_BITS); +} + /* * If error correction has been configured, returns true. */ bool verity_fec_is_enabled(struct dm_verity *v) { @@ -57,18 +69,10 @@ static u8 *fec_read_parity(struct dm_verity *v, u64 rsb= , int index, } =20 return res; } =20 -/* Loop over each preallocated buffer slot. */ -#define fec_for_each_prealloc_buffer(__i) \ - for (__i =3D 0; __i < DM_VERITY_FEC_BUF_PREALLOC; __i++) - -/* Loop over each extra buffer slot. */ -#define fec_for_each_extra_buffer(io, __i) \ - for (__i =3D DM_VERITY_FEC_BUF_PREALLOC; __i < DM_VERITY_FEC_BUF_MAX; __i= ++) - /* Loop over each allocated buffer. */ #define fec_for_each_buffer(io, __i) \ for (__i =3D 0; __i < (io)->nbufs; __i++) =20 /* Loop over each RS block in each allocated buffer. */ @@ -305,24 +309,23 @@ static int fec_read_bufs(struct dm_verity *v, struct = dm_verity_io *io, * Additional buffers are also allocated opportunistically to improve error * correction performance, but these aren't required to succeed. */ static struct dm_verity_fec_io *fec_alloc_and_init_io(struct dm_verity *v) { + const unsigned int max_nbufs =3D fec_max_nbufs(v); struct dm_verity_fec *f =3D v->fec; struct dm_verity_fec_io *fio; unsigned int n; =20 fio =3D mempool_alloc(&f->fio_pool, GFP_NOIO); fio->rs =3D mempool_alloc(&f->rs_pool, GFP_NOIO); =20 - memset(fio->bufs, 0, sizeof(fio->bufs)); - - fec_for_each_prealloc_buffer(n) - fio->bufs[n] =3D mempool_alloc(&f->prealloc_pool, GFP_NOIO); + static_assert(DM_VERITY_FEC_BUF_PREALLOC =3D=3D 1); + fio->bufs[0] =3D mempool_alloc(&f->prealloc_pool, GFP_NOIO); =20 /* try to allocate the maximum number of buffers */ - fec_for_each_extra_buffer(fio, n) { + for (n =3D 1; n < max_nbufs; n++) { fio->bufs[n] =3D kmem_cache_alloc(f->cache, GFP_NOWAIT); /* we can manage with even one buffer if necessary */ if (unlikely(!fio->bufs[n])) break; } @@ -460,16 +463,15 @@ void __verity_fec_finish_io(struct dm_verity_io *io) struct dm_verity_fec *f =3D io->v->fec; struct dm_verity_fec_io *fio =3D io->fec_io; =20 mempool_free(fio->rs, &f->rs_pool); =20 - fec_for_each_prealloc_buffer(n) - mempool_free(fio->bufs[n], &f->prealloc_pool); + static_assert(DM_VERITY_FEC_BUF_PREALLOC =3D=3D 1); + mempool_free(fio->bufs[0], &f->prealloc_pool); =20 - fec_for_each_extra_buffer(fio, n) - if (fio->bufs[n]) - kmem_cache_free(f->cache, fio->bufs[n]); + for (n =3D 1; n < fio->nbufs; n++) + kmem_cache_free(f->cache, fio->bufs[n]); =20 mempool_free(fio->output, &f->output_pool); =20 mempool_free(fio, &f->fio_pool); } @@ -732,11 +734,12 @@ int verity_fec_ctr(struct dm_verity *v) return -E2BIG; } =20 /* Preallocate some dm_verity_fec_io structures */ ret =3D mempool_init_kmalloc_pool(&f->fio_pool, num_online_cpus(), - sizeof(struct dm_verity_fec_io)); + struct_size((struct dm_verity_fec_io *)0, + bufs, fec_max_nbufs(v))); if (ret) { ti->error =3D "Cannot allocate FEC IO pool"; return ret; } =20 diff --git a/drivers/md/dm-verity-fec.h b/drivers/md/dm-verity-fec.h index b9488d1ddf14..84f8299673ff 100644 --- a/drivers/md/dm-verity-fec.h +++ b/drivers/md/dm-verity-fec.h @@ -17,13 +17,10 @@ #define DM_VERITY_FEC_MIN_RSN 231 /* ~10% space overhead */ =20 /* buffers for deinterleaving and decoding */ #define DM_VERITY_FEC_BUF_PREALLOC 1 /* buffers to preallocate */ #define DM_VERITY_FEC_BUF_RS_BITS 4 /* 1 << RS blocks per buffer */ -/* we need buffers for at most 1 << block size RS blocks */ -#define DM_VERITY_FEC_BUF_MAX \ - (1 << (PAGE_SHIFT - DM_VERITY_FEC_BUF_RS_BITS)) =20 #define DM_VERITY_OPT_FEC_DEV "use_fec_from_device" #define DM_VERITY_OPT_FEC_BLOCKS "fec_blocks" #define DM_VERITY_OPT_FEC_START "fec_start" #define DM_VERITY_OPT_FEC_ROOTS "fec_roots" @@ -50,14 +47,21 @@ struct dm_verity_fec { =20 /* per-bio data */ struct dm_verity_fec_io { struct rs_control *rs; /* Reed-Solomon state */ int erasures[DM_VERITY_FEC_MAX_RSN]; /* erasures for decode_rs8 */ - u8 *bufs[DM_VERITY_FEC_BUF_MAX]; /* bufs for deinterleaving */ - unsigned int nbufs; /* number of buffers allocated */ u8 *output; /* buffer for corrected output */ unsigned int level; /* recursion level */ + unsigned int nbufs; /* number of buffers allocated */ + /* + * Buffers for deinterleaving RS blocks. Each buffer has space for + * the data bytes of (1 << DM_VERITY_FEC_BUF_RS_BITS) RS blocks. The + * array length is fec_max_nbufs(v), and we try to allocate that many + * buffers. However, in low-memory situations we may be unable to + * allocate all buffers. 'nbufs' holds the number actually allocated. + */ + u8 *bufs[]; }; =20 #ifdef CONFIG_DM_VERITY_FEC =20 /* each feature parameter requires a value */ --=20 2.52.0