Re: [PATCH] cxl/region: Use do_div() for 64-bit modulo operation

[Dave Jiang <dave.jiang@intel.com>]

On 1/16/26 9:47 PM, Alison Schofield wrote:
> div64_u64_rem() was the wrong choice for doing a modulo operation
> and it was used incorrectly, causing a kernel oops by passing NULL
> as the remainder parameter. Replace it with the do_div() helper
> that does the intended math (gran_offset = offset % gran) and is
> architecture safe.
> 
> This bug appeared during testing of unaligned address translations.
> The visibility to userspace would be limited to folks doing poison
> injection or clear by HPA on unaligned regions.
> 
> Fixes: 78b50b598462 ("cxl/region: Translate HPA to DPA and memdev in unaligned regions")
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

Thanks Alison. I'll get this applied to next
> ---
>  drivers/cxl/core/region.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index d5979000fba1..96888d87a8df 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3324,6 +3324,7 @@ static int unaligned_region_offset_to_dpa_result(struct cxl_region *cxlr,
>  	u64 interleave_width, interleave_index;
>  	u64 gran, gran_offset, dpa_offset;
>  	u64 hpa = p->res->start + offset;
> +	u64 tmp = offset;
>  
>  	/*
>  	 * Unaligned addresses are not algebraically invertible. Calculate
> @@ -3333,7 +3334,7 @@ static int unaligned_region_offset_to_dpa_result(struct cxl_region *cxlr,
>  	gran = cxld->interleave_granularity;
>  	interleave_width = gran * cxld->interleave_ways;
>  	interleave_index = div64_u64(offset, interleave_width);
> -	gran_offset = div64_u64_rem(offset, gran, NULL);
> +	gran_offset = do_div(tmp, gran);
>  
>  	dpa_offset = interleave_index * gran + gran_offset;
>  
> 
> base-commit: 78b50b5984629d362f826e9615ce4599f429716e