Re: [PATCH v6 1/4] libata: Safely overwrite attached page in WRITE SAME xlat

Tom Yan
2016-08-22T21:20:08Z

On 22 August 2016 at 04:23, Shaun Tancheff <shaun@tancheff.com> wrote:
> Safely overwriting the attached page to ATA format from the SCSI formatted
> variant.
>
> Signed-off-by: Shaun Tancheff <shaun.tancheff@seagate.com>
> ---
> v6:
> - Fix bisect bug reported by Tom Yan <tom.ty89@gmail.com>
> - Change to use sg_copy_from_buffer as per Christoph Hellwig <hch@lst.de>
> v5:
> - Added prep patch to work with non-page aligned scatterlist pages
> and use kmap_atomic() to lock page during modification.
>
> drivers/ata/libata-scsi.c | 56 ++++++++++++++++++++++++++++++++++++++++++-----
> include/linux/ata.h | 26 ----------------------
> 2 files changed, 51 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index e207b33..7990cb2 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -3282,6 +3282,54 @@ static unsigned int ata_scsi_pass_thru(struct ata_queued_cmd *qc)
> return 1;
> }
>
> +/**
> + * ata_format_dsm_trim_descr() - SATL Write Same to DSM Trim
> + * @cmd: SCSI command being translated
> + * @num: Maximum number of entries (nominally 64).
> + * @sector: Starting sector
> + * @count: Total Range of request
> + *
> + * Rewrite the WRITE SAME descriptor to be a DSM TRIM little-endian formatted
> + * descriptor.
> + *
> + * Upto 64 entries of the format:
> + * 63:48 Range Length
> + * 47:0 LBA
> + *
> + * Range Length of 0 is ignored.
> + * LBA's should be sorted order and not overlap.
> + *
> + * NOTE: this is the same format as ADD LBA(S) TO NV CACHE PINNED SET
> + */
> +static unsigned int ata_format_dsm_trim_descr(struct scsi_cmnd *cmd, u32 num,
> + u64 sector, u32 count)
> +{
> + __le64 *buffer;
> + u32 i = 0, used_bytes;
> + unsigned long flags;
> +
> + BUILD_BUG_ON(512 > ATA_SCSI_RBUF_SIZE);

Why do we want to check "512" (a literal number) against
ATA_SCSI_RBUF_SIZE here?

> +
> + spin_lock_irqsave(&ata_scsi_rbuf_lock, flags);
> + buffer = ((void *)ata_scsi_rbuf);
> + while (i < num) {
> + u64 entry = sector |
> + ((u64)(count > 0xffff ? 0xffff : count) << 48);
> + buffer[i++] = __cpu_to_le64(entry);
> + if (count <= 0xffff)
> + break;
> + count -= 0xffff;
> + sector += 0xffff;
> + }
> +
> + used_bytes = ALIGN(i * 8, 512);
> + memset(buffer + i, 0, used_bytes - i * 8);
> + sg_copy_from_buffer(scsi_sglist(cmd), scsi_sg_count(cmd), buffer, 512);
> + spin_unlock_irqrestore(&ata_scsi_rbuf_lock, flags);
> +
> + return used_bytes;
> +}
> +
> static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
> {
> struct ata_taskfile *tf = &qc->tf;
> @@ -3290,8 +3338,8 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
> const u8 *cdb = scmd->cmnd;
> u64 block;
> u32 n_block;
> + const u32 trmax = ATA_MAX_TRIM_RNUM;
> u32 size;
> - void *buf;
> u16 fp;
> u8 bp = 0xff;
>
> @@ -3319,10 +3367,8 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
> if (!scsi_sg_count(scmd))
> goto invalid_param_len;
>
> - buf = page_address(sg_page(scsi_sglist(scmd)));
> -
> - if (n_block <= 65535 * ATA_MAX_TRIM_RNUM) {
> - size = ata_set_lba_range_entries(buf, ATA_MAX_TRIM_RNUM, block, n_block);
> + if (n_block <= 0xffff * trmax) {
> + size = ata_format_dsm_trim_descr(scmd, trmax, block, n_block);
> } else {
> fp = 2;
> goto invalid_fld;
> diff --git a/include/linux/ata.h b/include/linux/ata.h
> index adbc812..45a1d71 100644
> --- a/include/linux/ata.h
> +++ b/include/linux/ata.h
> @@ -1071,32 +1071,6 @@ static inline void ata_id_to_hd_driveid(u16 *id)
> #endif
> }
>
> -/*
> - * Write LBA Range Entries to the buffer that will cover the extent from
> - * sector to sector + count. This is used for TRIM and for ADD LBA(S)
> - * TO NV CACHE PINNED SET.
> - */
> -static inline unsigned ata_set_lba_range_entries(void *_buffer,
> - unsigned num, u64 sector, unsigned long count)
> -{
> - __le64 *buffer = _buffer;
> - unsigned i = 0, used_bytes;
> -
> - while (i < num) {
> - u64 entry = sector |
> - ((u64)(count > 0xffff ? 0xffff : count) << 48);
> - buffer[i++] = __cpu_to_le64(entry);
> - if (count <= 0xffff)
> - break;
> - count -= 0xffff;
> - sector += 0xffff;
> - }
> -
> - used_bytes = ALIGN(i * 8, 512);
> - memset(buffer + i, 0, used_bytes - i * 8);
> - return used_bytes;
> -}
> -
> static inline bool ata_ok(u8 status)
> {
> return ((status & (ATA_BUSY | ATA_DRDY | ATA_DF | ATA_DRQ | ATA_ERR))
> --
> 2.9.3
>