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

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

[Vasily Gorbik]

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);
 	}
 	kernel_fpu_begin(&vxstate, KERNEL_VXR_V16V23);
 	fpu_vlvgf(16, (__force u32)sum, 1);
-- 
2.53.0

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

[Heiko Carstens]

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.

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

[Vasily Gorbik]

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(-)

Applied