Re: [PATCH V5 6/9] dax/fsdev: fail probe on invalid pgmap offset

["Gupta, Pankaj" <pankaj.gupta@amd.com>]

> From: John Groves <John@Groves.net>
>
> Convert the WARN_ON to a fatal error when pgmap_phys > phys. This
> condition means the remapped region starts after the device's data
> region, which is an impossible state. Previously the probe continued
> with data_offset=0, leaving virt_addr silently misaligned. Now probe
> returns -EINVAL with a diagnostic message.
>
> Fixes: 759455848df0b ("dax: Save the kva from memremap")
>
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> Reviewed-by: Alison Schofield <alison.schofield@intel.com>
> Signed-off-by: John Groves <john@groves.net>

Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>

> ---
>   drivers/dax/fsdev.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dax/fsdev.c b/drivers/dax/fsdev.c
> index 07de6bfbbf673..71d2bee1e2805 100644
> --- a/drivers/dax/fsdev.c
> +++ b/drivers/dax/fsdev.c
> @@ -320,8 +320,12 @@ static int fsdev_dax_probe(struct dev_dax *dev_dax)
>   		u64 phys = dev_dax->ranges[0].range.start;
>   		u64 pgmap_phys = pgmap[0].range.start;
>   
> -		if (!WARN_ON(pgmap_phys > phys))
> -			data_offset = phys - pgmap_phys;
> +		if (pgmap_phys > phys) {
> +			dev_err(dev, "pgmap start %#llx exceeds data start %#llx\n",
> +				pgmap_phys, phys);
> +			return -EINVAL;
> +		}
> +		data_offset = phys - pgmap_phys;
>   
>   		pr_debug("%s: offset detected phys=%llx pgmap_phys=%llx offset=%llx\n",
>   		       __func__, phys, pgmap_phys, data_offset);