Re: [PATCH] scsi: sd_zbc: Limit the report zones buffer size to UIO_MAXIOV

[Siwinski, Steve]

On 4/18/2025 5:29 PM, Damien Le Moal wrote:
> On 4/19/25 05:46, SSiwinski@xxxxxxxx wrote:
> > "Christoph Hellwig" <hch@xxxxxxxxxxxxx> wrote on 04/14/2025 01:52:31 AM:
> >
> > > On Fri, Apr 11, 2025 at 04:36:00PM -0400, Steve Siwinski wrote:
> > > > The report zones buffer size is currently limited by the HBA's
> > > > maximum segment count to ensure the buffer can be mapped. However,
> > > > the user-space SG_IO interface further limits the number of iovec
> > > > entries to UIO_MAXIOV when allocating a bio.
> > >
> > > Why does the userspace SG_IO interface matter here?
> > > sd_zbc_alloc_report_buffer is only used for the in-kernel
> > > ->report_zones call.
> >
> > I was referring to the userspace SG_IO limitation (UIO_MAXIOV) in
> > bio_kmalloc(), which gets called when the report zones command is
> > executed and the buffer mapped in bio_map_kern().
> >
> > Perhaps my wording here was poor and this is really a limitation of bio?
>
> sd_zbc_alloc_report_buffer() is called only from sd_zbc_report_zones() which is
> the disk ->report_zones() operations, which is NOT called for passthrough
> commands. So modifying sd_zbc_alloc_report_buffer() will not help in any way
> solving your issue with an SG_IO passthrough report zones command issued by the
> user.
>
> For reference, libzbc uses ioctl(SG_GET_SG_TABLESIZE) * sysconf(_SC_PAGESIZE) as
> the max buffer size and allocates page aligned buffers to avoid these SG_IO
> buffer mapping limitations.

My issue is not with passthough report zones.

The report zones command is failing on driver load and causing the drive 
to fail to appear as a block device. If queue_max_segments is set to a 
value over 1024, then nr_vecs in bio_alloc() will be greater than 
UIO_MAXIOV and bio_alloc() will return NULL.

This causes the error.
```
sd 8:0:0:0: [sdb] REPORT ZONES start lba 0 failed
sd 8:0:0:0: [sdb] REPORT ZONES: Result: hostbyte=0xff driverbyte=DRIVER_OK
sdb: failed to revalidate zones
```

You can reproduce this by setting the max_sgl_entries parameter to 2k or 
greater in the mpt3sas driver. Other drivers can also reproduce this 
behavior.


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