Re: [PATCH] cxl/region：Fix overflow issue in alloc_hpa()

[Alison Schofield <alison.schofield@intel.com>]

On Wed, Jan 24, 2024 at 05:15:26PM +0800, Quanquan Cao wrote:
> Creating a region with 16 memory devices caused a problem. The div_u64_rem
> function, used for dividing an unsigned 64-bit number by a 32-bit one,
> faced an issue when SZ_256M * p->interleave_ways. The result surpassed
> the maximum limit of the 32-bit divisor (4G), leading to an overflow
> and a remainder of 0.
> note: At this point, p->interleave_ways is 16, meaning 16 * 256M = 4G
> 
> To fix this issue, I replaced the div_u64_rem function with div64_u64_rem
> and adjusted the type of the remainder.

Good find!  Should this have a Fixes Tag?

Reviewed-by: Alison Schofield <alison.schofield@intel.com>


> 
> Signed-off-by: Quanquan Cao <caoqq@fujitsu.com>
> ---
>  drivers/cxl/core/region.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 0f05692bfec3..ce0e2d82bb2b 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -525,7 +525,7 @@ static int alloc_hpa(struct cxl_region *cxlr, resource_size_t size)
>  	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
>  	struct cxl_region_params *p = &cxlr->params;
>  	struct resource *res;
> -	u32 remainder = 0;
> +	u64 remainder = 0;
>  
>  	lockdep_assert_held_write(&cxl_region_rwsem);
>  
> @@ -545,7 +545,7 @@ static int alloc_hpa(struct cxl_region *cxlr, resource_size_t size)
>  	    (cxlr->mode == CXL_DECODER_PMEM && uuid_is_null(&p->uuid)))
>  		return -ENXIO;
>  
> -	div_u64_rem(size, SZ_256M * p->interleave_ways, &remainder);
> +	div64_u64_rem(size, (u64)SZ_256M * p->interleave_ways, &remainder);
>  	if (remainder)
>  		return -EINVAL;
>  
> -- 
> 2.43.0
> 
>