Re: [PATCH v12 3/3] ufs: set max_bio_bytes with queue max sectors

[Changheun Lee <nanich.lee@samsung.com>]

> On 6/3/21 10:03 PM, Changheun Lee wrote:
> > Set max_bio_bytes same with queue max sectors. It will lead to fast bio
> > submit when bio size is over than queue max sectors. And it might be helpful
> > to align submit bio size in some case.
> > 
> > Signed-off-by: Changheun Lee <nanich.lee@samsung.com>
> > ---
> >  drivers/scsi/ufs/ufshcd.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> > index 3eb54937f1d8..37365a726517 100644
> > --- a/drivers/scsi/ufs/ufshcd.c
> > +++ b/drivers/scsi/ufs/ufshcd.c
> > @@ -4858,6 +4858,7 @@ static int ufshcd_slave_configure(struct scsi_device *sdev)
> >  {
> >  	struct ufs_hba *hba = shost_priv(sdev->host);
> >  	struct request_queue *q = sdev->request_queue;
> > +	unsigned int max_bio_bytes;
> >  
> >  	blk_queue_update_dma_pad(q, PRDT_DATA_BYTE_COUNT_PAD - 1);
> >  	if (hba->quirks & UFSHCD_QUIRK_ALIGN_SG_WITH_PAGE_SIZE)
> > @@ -4868,6 +4869,10 @@ static int ufshcd_slave_configure(struct scsi_device *sdev)
> >  
> >  	ufshcd_crypto_setup_rq_keyslot_manager(hba, q);
> >  
> > +	if (!check_shl_overflow(queue_max_sectors(q),
> > +				SECTOR_SHIFT, &max_bio_bytes))
> > +		blk_queue_max_bio_bytes(q, max_bio_bytes);
> > +
> >  	return 0;
> >  }
> 
> Just like previous versions of this patch series, this approach will
> trigger data corruption if dm-crypt is stacked on top of the UFS driver
> since ufs_max_sectors << SECTOR_SHIFT = 1024 * 512 is less than the size
> of the dm-crypt buffer (BIO_MAX_VECS << PAGE_SHIFT = 256 * 4096).

max_bio_bytes can't be smaller than "BIO_MAX_VECS * PAGE_SIZE". Large value
will be selected between input parameter and  "BIO_MAX_VECS * PAGE_SIZE" in
blk_queue_max_bio_bytes(). I think bio max size should be larger than
"BIO_MAX_VECS * PAGE_SIZE" for kernel stability.

void blk_queue_max_bio_bytes(struct request_queue *q, unsigned int bytes)
{
	struct queue_limits *limits = &q->limits;
	unsigned int max_bio_bytes = round_up(bytes, PAGE_SIZE);

	limits->max_bio_bytes = max_t(unsigned int, max_bio_bytes,
				      BIO_MAX_VECS * PAGE_SIZE);
}
EXPORT_SYMBOL(blk_queue_max_bio_bytes);

> 
> I am not recommending to increase max_sectors for the UFS driver. We
> need a solution that is independent of the dm-crypt internals.
> 
> Bart.

No need to increase max_sectors in driver to set max_bio_bytes. There are
no dependency with dm-crypt I think.

Thank you,
Changheun Lee