[PATCH v2 1/2] ata: libata-scsi: fix DSM TRIM for sector sizes larger than 2048 bytes

[Niklas Cassel <cassel@kernel.org>]

ata_scsi_write_same_xlat() translates a SCSI WRITE SAME command with the
UNMAP bit set into an ATA DATA SET MANAGEMENT TRIM command.  The TRIM
descriptor is built by ata_format_dsm_trim_descr() into the 2048-byte
ata_scsi_rbuf staging buffer, and the number of bytes copied is compared
against the logical sector size by the caller:

	size = ata_format_dsm_trim_descr(scmd, trmax, block, n_block);
	if (size != len)		/* len == sdp->sector_size */
		goto invalid_param_len;

ata_format_dsm_trim_descr() clamps the copy length to ATA_SCSI_RBUF_SIZE
(2048).  On a device whose logical sector size exceeds that (e.g. a 4Kn
device, where sector_size == 4096) the function can never return more than
2048, while the caller expects it to return sector_size.  The comparison
therefore always fails, so every TRIM is rejected with "Parameter list
length error" and WARN_ON() splats on each attempt.  TRIM / discard is
thus completely broken on such devices.

The descriptor was incorrectly sized from the logical sector size.  A DSM
TRIM payload is a list of 512-byte pages, each holding up to
ATA_MAX_TRIM_RNUM (64) LBA Range Entries, and is independent of the logical
sector size.  The Block Limits VPD page already advertises a single such
page as the maximum WRITE SAME length (65535 * ATA_MAX_TRIM_RNUM logical
blocks), so the block layer never sends a request that needs more than one
page.

Emit exactly one 512-byte page, independent of the logical sector size,
and transfer only that page (COUNT == 1).  For a 512-byte-sector device
this is unchanged; devices with larger logical sectors now work instead of
failing every TRIM.

Reviewed-by: Hannes Reinecke <hare@kernel.org>
Fixes: ef2d7392c4ec ("libata: SCT Write Same / DSM Trim")
Cc: stable@vger.kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 drivers/ata/libata-scsi.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index d54ec1631e9a..429b03a08071 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -3447,17 +3447,13 @@ static unsigned int ata_scsi_pass_thru(struct ata_queued_cmd *qc)
 static size_t ata_format_dsm_trim_descr(struct scsi_cmnd *cmd, u32 trmax,
 					u64 sector, u32 count)
 {
-	struct scsi_device *sdp = cmd->device;
-	size_t len = sdp->sector_size;
+	size_t len = ATA_SECT_SIZE;
 	size_t r;
 	__le64 *buf;
 	u32 i = 0;
 	unsigned long flags;
 
-	WARN_ON(len > ATA_SCSI_RBUF_SIZE);
-
-	if (len > ATA_SCSI_RBUF_SIZE)
-		len = ATA_SCSI_RBUF_SIZE;
+	BUILD_BUG_ON(ATA_SECT_SIZE > ATA_SCSI_RBUF_SIZE);
 
 	spin_lock_irqsave(&ata_scsi_rbuf_lock, flags);
 	buf = ((void *)ata_scsi_rbuf);
@@ -3492,13 +3488,11 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
 {
 	struct ata_taskfile *tf = &qc->tf;
 	struct scsi_cmnd *scmd = qc->scsicmd;
-	struct scsi_device *sdp = scmd->device;
-	size_t len = sdp->sector_size;
 	struct ata_device *dev = qc->dev;
 	const u8 *cdb = scmd->cmnd;
 	u64 block;
 	u32 n_block;
-	const u32 trmax = len >> 3;
+	const u32 trmax = ATA_MAX_TRIM_RNUM;
 	u32 size;
 	u16 fp;
 	u8 bp = 0xff;
@@ -3542,13 +3536,13 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
 		goto invalid_param_len;
 
 	/*
-	 * size must match sector size in bytes
-	 * For DATA SET MANAGEMENT TRIM in ACS-2 nsect (aka count)
-	 * is defined as number of 512 byte blocks to be transferred.
+	 * The TRIM descriptor is a single 512-byte page, which is the maximum
+	 * WRITE SAME length advertised in the Block Limits VPD page. For DATA
+	 * SET MANAGEMENT TRIM the COUNT field (aka nsect) is the number of
+	 * 512-byte blocks to be transferred.
 	 */
-
 	size = ata_format_dsm_trim_descr(scmd, trmax, block, n_block);
-	if (size != len)
+	if (size != ATA_SECT_SIZE)
 		goto invalid_param_len;
 
 	if (ata_ncq_enabled(dev) && ata_fpdma_dsm_supported(dev)) {
@@ -3574,6 +3568,12 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
 		     ATA_TFLAG_WRITE;
 
 	ata_qc_set_pc_nbytes(qc);
+	/*
+	 * The DSM TRIM payload is a single 512-byte page, which may be smaller
+	 * than the WRITE SAME data-out buffer (one logical block); only
+	 * transfer that page so the length matches the COUNT field.
+	 */
+	qc->nbytes = size;
 
 	return 0;
 
-- 
2.55.0