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

[Shaun Tancheff]

On Mon, Aug 22, 2016 at 2:27 PM, Tom Yan <tom.ty89@xxxxxxxxx> wrote:
> On 22 August 2016 at 12:23, Shaun Tancheff <shaun@xxxxxxxxxxxx> wrote:
>> Safely overwriting the attached page to ATA format from the SCSI formatted
>> variant.
>>
>> Signed-off-by: Shaun Tancheff <shaun.tancheff@xxxxxxxxxxx>
>> ---
>> v6:
>>  - Fix bisect bug reported by Tom Yan <tom.ty89@xxxxxxxxx>
>>  - Change to use sg_copy_from_buffer as per Christoph Hellwig <hch@xxxxxx>
>> 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);
>> +
>> +       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;
>
> This does not seem like a good idea.
>
>>         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) {
>
> Note that the limit here would always be the advertised Maximum Write
> Same Length (ata_scsiop_inq_b0). It would be best for them to look the
> same. Besides, it doesn't seem necessary to create this trmax anyway.

It is entirely a style thing. I tend to prefer hex when describing an interface
that specifies number of bits. The trmax is just to keep the following line
under 80 chars.
I am not tied to either. I can change it if people really find it confusing.

>> +               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
>>



-- 
Shaun Tancheff