Re: [PATCH] s390/checksum: Fix csum_partial() without vector facility

[Heiko Carstens <hca@linux.ibm.com>]

On Wed, Jul 08, 2026 at 12:02:14PM +0200, Vasily Gorbik wrote:
> Currently csum_partial() calls csum_copy() with copy=false and dst=NULL.
> On machines without the vector facility, csum_copy() falls back to
> cksm(dst, ...), causing the checksum to be calculated from address zero
> instead of the source buffer.
> 
> The VX implementation already checksums data loaded from src. Make the
> fallback do the same by passing src to cksm().
> 
> Fixes: dcd3e1de9d17 ("s390/checksum: provide csum_partial_copy_nocheck()")
> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
> ---
>  arch/s390/lib/csum-partial.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/s390/lib/csum-partial.c b/arch/s390/lib/csum-partial.c
> index 458abd9bac70..9d74ceff136c 100644
> --- a/arch/s390/lib/csum-partial.c
> +++ b/arch/s390/lib/csum-partial.c
> @@ -23,7 +23,7 @@ static __always_inline __wsum csum_copy(void *dst, const void *src, int len, __w
>  	if (!cpu_has_vx()) {
>  		if (copy)
>  			memcpy(dst, src, len);
> -		return cksm(dst, len, sum);
> +		return cksm(src, len, sum);

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>

But at least that also tells us that this code never worked on pre z13.