linux-kernel - Re: [PATCH] scsi: sd_zbc: Limit the report zones buffer size to UIO

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Message-ID: <Z_yinytV0e_BbNrF@infradead.org>
Date: Sun, 13 Apr 2025 22:52:31 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Steve Siwinski <stevensiwinski@...il.com>
Cc: James.Bottomley@...senpartnership.com, martin.petersen@...cle.com,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	bgrove@...o.com, Steve Siwinski <ssiwinski@...o.com>,
	Damien Le Moal <dlemoal@...nel.org>
Subject: Re: [PATCH] scsi: sd_zbc: Limit the report zones buffer size to
 UIO_MAXIOV

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.

> 
> To avoid allocation of buffers too large to be mapped, further
> restrict the maximum buffer size to UIO_MAXIOV * PAGE_SIZE.
> 
> This ensures that the buffer size complies with both kernel
> and user-space constraints.
> 
> Signed-off-by: Steve Siwinski <ssiwinski@...o.com>
> ---
>  drivers/scsi/sd_zbc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/scsi/sd_zbc.c b/drivers/scsi/sd_zbc.c
> index 7a447ff600d2..a19e76ec8fb6 100644
> --- a/drivers/scsi/sd_zbc.c
> +++ b/drivers/scsi/sd_zbc.c
> @@ -180,12 +180,15 @@ static void *sd_zbc_alloc_report_buffer(struct scsi_disk *sdkp,
>  	 * Furthermore, since the report zone command cannot be split, make
>  	 * sure that the allocated buffer can always be mapped by limiting the
>  	 * number of pages allocated to the HBA max segments limit.
> +	 * Since max segments can be larger than the max sgio entries, further
> +	 * limit the allocated buffer to the UIO_MAXIOV.
>  	 */
>  	nr_zones = min(nr_zones, sdkp->zone_info.nr_zones);
>  	bufsize = roundup((nr_zones + 1) * 64, SECTOR_SIZE);
>  	bufsize = min_t(size_t, bufsize,
>  			queue_max_hw_sectors(q) << SECTOR_SHIFT);
>  	bufsize = min_t(size_t, bufsize, queue_max_segments(q) << PAGE_SHIFT);
> +	bufsize = min_t(size_t, bufsize, UIO_MAXIOV * PAGE_SIZE);
>  
>  	while (bufsize >= SECTOR_SIZE) {
>  		buf = kvzalloc(bufsize, GFP_KERNEL | __GFP_NORETRY);
> -- 
> 2.43.5
> 
> 
---end quoted text---