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Wed, 24 Jun 2026 10:29:39 -0700 (PDT) Received: from twshared11639.02.snb2.facebook.com (2620:10d:c085:108::4) by mail.thefacebook.com (2620:10d:c08b:78::c78f) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.2562.41; Wed, 24 Jun 2026 17:29:38 +0000 Received: by devbig197.nha3.facebook.com (Postfix, from userid 544533) id 4863A23C452BD; Wed, 24 Jun 2026 10:09:08 -0700 (PDT) From: Keith Busch To: , CC: , , , , , , Keith Busch Subject: [PATCH v3 3/5] loop: set dma_alignment from the backing file for direct I/O Date: Wed, 24 Jun 2026 10:09:03 -0700 Message-ID: <20260624170905.3972095-4-kbusch@meta.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260624170905.3972095-1-kbusch@meta.com> References: <20260624170905.3972095-1-kbusch@meta.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-FB-Internal: Safe Content-Type: text/plain X-Authority-Analysis: v=2.4 cv=eoTvCIpX c=1 sm=1 tr=0 ts=6a3c1403 cx=c_pps a=CB4LiSf2rd0gKozIdrpkBw==:117 a=CB4LiSf2rd0gKozIdrpkBw==:17 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=7x6HtfJdh03M6CCDgxCd:22 a=JnKecZnUtZousrUlYMGU:22 a=VwQbUJbxAAAA:8 a=w3YrK2sSALtTPwlh2GsA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjI0MDE0NiBTYWx0ZWRfX21yXRT0iWsP0 /OJgLCwSBiW4VoqM7zs4d7qwDjyFYgLr9miYB3n95rAz1mrBvUqntDqmQl1JrabXvoP1CT7oTKx g9yqddQV/H1YN9dUpDOWA78fatHD8tZO/9VYniXQriaDZbCqqwUxvfNrr1hTGSMo7g7yJZ92YmZ EdUv3ye5VZufRahK7SxLCx+0ZuFMCIaq7wel869LS4lgnzuHIGrm6GA8hUL4QNnb2jokcx0ndro OxsviHMynuUOLYDyBFmp5vN8IvLT4IUil53Pvj79mU2O9o7mk6O/w+LopGO2FcYuKeomK4HMID5 kIJjn+R79aHf/tNeQwd6m6afNP3O0YYhzuwPk85+MPs6QSg7kENfKa45zfm0SXVOR828nMhMRKJ xyVWsWP6OSWtiwpoPpr97Uad+mdLhQ== X-Proofpoint-ORIG-GUID: 3jpuO6Jwz6NQdii2Yd2or4QxEBxT_kPh X-Proofpoint-Spam-Info: AW1haW4tMjYwNjI0MDE0NiBTYWx0ZWRfX3FQxmmItm/qy L7A3lc30AX1uEVwaYa7cqV3O+CBdzfdUaSddaKWlsc29ayBabT3f41/nHwmIDDjXkKoazg7dhuK /UcKbPhHdEgpI+4zoUf3PBRH/mrUM28= X-Proofpoint-GUID: 3jpuO6Jwz6NQdii2Yd2or4QxEBxT_kPh X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-24_03,2026-06-24_01,2025-10-01_01 From: Keith Busch Direct I/O user pages are forwarded to the backing file unchanged, so the backing's DMA alignment requirement applies to them. Track the backing file's dio_mem_align and advertise it as the loop device's dma_alignment if it is larger than the default so we advertise proper limits and misaligned I/O is rejected early instead of being dispatched to the backend. Signed-off-by: Keith Busch --- drivers/block/loop.c | 46 ++++++++++++++++++++++++++++++++++++-------- 1 file changed, 38 insertions(+), 8 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 310de0463beb1..5fe61d542f8b7 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -54,6 +54,7 @@ struct loop_device { =20 struct file *lo_backing_file; unsigned int lo_min_dio_size; + unsigned int lo_dio_mem_align; struct block_device *lo_device; =20 gfp_t old_gfp_mask; @@ -447,26 +448,37 @@ static void loop_reread_partitions(struct loop_devi= ce *lo) __func__, lo->lo_number, lo->lo_file_name, rc); } =20 -static unsigned int loop_query_min_dio_size(struct loop_device *lo) +static void loop_update_dio_alignment(struct loop_device *lo) { struct file *file =3D lo->lo_backing_file; struct block_device *sb_bdev =3D file->f_mapping->host->i_sb->s_bdev; struct kstat st; =20 /* - * Use the minimal dio alignment of the file system if provided. + * Use the dio alignment of the file system if provided. The incomoing + * request's bio_vec is forwarded to the backing file unchanged, so its + * required memory alignment becomes the device's dma_alignment when + * used for direct-io. */ if (!vfs_getattr(&file->f_path, &st, STATX_DIOALIGN, 0) && - (st.result_mask & STATX_DIOALIGN)) - return st.dio_offset_align; + (st.result_mask & STATX_DIOALIGN)) { + lo->lo_min_dio_size =3D st.dio_offset_align; + lo->lo_dio_mem_align =3D st.dio_mem_align - 1; + return; + } =20 /* * In a perfect world this wouldn't be needed, but as of Linux 6.13 onl= y * a handful of file systems support the STATX_DIOALIGN flag. */ - if (sb_bdev) - return bdev_logical_block_size(sb_bdev); - return SECTOR_SIZE; + if (sb_bdev) { + lo->lo_min_dio_size =3D bdev_logical_block_size(sb_bdev); + lo->lo_dio_mem_align =3D bdev_dma_alignment(sb_bdev); + return; + } + + lo->lo_min_dio_size =3D SECTOR_SIZE; + lo->lo_dio_mem_align =3D SECTOR_SIZE - 1; } =20 static inline int is_loop_device(struct file *file) @@ -509,7 +521,7 @@ static void loop_assign_backing_file(struct loop_devi= ce *lo, struct file *file) lo->old_gfp_mask & ~(__GFP_IO | __GFP_FS)); if (lo->lo_backing_file->f_flags & O_DIRECT) lo->lo_flags |=3D LO_FLAGS_DIRECT_IO; - lo->lo_min_dio_size =3D loop_query_min_dio_size(lo); + loop_update_dio_alignment(lo); } =20 static int loop_check_backing_file(struct file *file) @@ -940,6 +952,19 @@ static unsigned int loop_default_blocksize(struct lo= op_device *lo) return SECTOR_SIZE; } =20 +static void loop_set_dma_limit(struct loop_device *lo, struct queue_limi= ts *lim) +{ + /* + * Direct I/O forwards the user pages to the backing file unchanged, so + * track the backing's DMA alignment requirement as the mode is toggled= . + */ + if (lo->lo_flags & LO_FLAGS_DIRECT_IO) + lim->dma_alignment =3D max_t(unsigned int, lo->lo_dio_mem_align, + SECTOR_SIZE - 1); + else + lim->dma_alignment =3D SECTOR_SIZE - 1; +} + static void loop_update_limits(struct loop_device *lo, struct queue_limi= ts *lim, unsigned int bsize) { @@ -961,6 +986,7 @@ static void loop_update_limits(struct loop_device *lo= , struct queue_limits *lim, lim->logical_block_size =3D bsize; lim->physical_block_size =3D bsize; lim->io_min =3D bsize; + loop_set_dma_limit(lo, lim); lim->features &=3D ~(BLK_FEAT_WRITE_CACHE | BLK_FEAT_ROTATIONAL); if (file->f_op->fsync && !(lo->lo_flags & LO_FLAGS_READ_ONLY)) lim->features |=3D BLK_FEAT_WRITE_CACHE; @@ -1416,6 +1442,7 @@ static int loop_set_dio(struct loop_device *lo, uns= igned long arg) { bool use_dio =3D !!arg; unsigned int memflags; + struct queue_limits lim; =20 if (lo->lo_state !=3D Lo_bound) return -ENXIO; @@ -1434,6 +1461,9 @@ static int loop_set_dio(struct loop_device *lo, uns= igned long arg) lo->lo_flags |=3D LO_FLAGS_DIRECT_IO; else lo->lo_flags &=3D ~LO_FLAGS_DIRECT_IO; + lim =3D queue_limits_start_update(lo->lo_queue); + loop_set_dma_limit(lo, &lim); + queue_limits_commit_update(lo->lo_queue, &lim); blk_mq_unfreeze_queue(lo->lo_queue, memflags); return 0; } --=20 2.53.0-Meta