Re: [PATCH v3 12/13] s390/qdio_setup: Use kmalloc() for the SSQD request

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] s390/cio: CHSC command block alignment broken by kmalloc()
--

commit 81f70c4032ffb64f5a06eb9ca6de3a70bfe61e77
Author: Mike Rapoport (Microsoft) <rppt@kernel.org>

s390/qdio_setup: Use kmalloc() for the SSQD request

This commit replaces the use of __get_free_page() with kmalloc() and
free_page() with kfree() for the SSQD request block allocation. It assumes
there is no special requirement for the memory to come directly from the
page allocator.

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com

> diff --git a/drivers/s390/cio/qdio_setup.c b/drivers/s390/cio/qdio_setup.c
> index d8e9c0872d15d..e1c5c6a8b3b27 100644
> --- a/drivers/s390/cio/qdio_setup.c
> +++ b/drivers/s390/cio/qdio_setup.c
[ ... ]
> @@ -249,7 +249,7 @@ int qdio_setup_get_ssqd(struct qdio_irq *irq_ptr,
>  
>  	DBF_EVENT("getssqd:%4x", schid->sch_no);
>  	if (!irq_ptr) {
> -		ssqd = (struct chsc_ssqd_area *)__get_free_page(GFP_KERNEL);
> +		ssqd = kmalloc(PAGE_SIZE, GFP_KERNEL);

[Severity: High]
Does this kmalloc() call break the strict 4K-byte physical page alignment
required for the CHSC command block?

While __get_free_page() guarantees page alignment, kmalloc(PAGE_SIZE) does
not. When memory debugging features like KASAN or SLAB_RED_ZONE are enabled,
metadata is inserted before the object, shifting the payload pointer away
from the page boundary.

Could passing this unaligned pointer to the hardware via chsc_ssqd() trigger
a hardware specification exception (PGM_SPECIFICATION) and kernel crash
during device initialization? 

It is also worth noting that this same pattern seems to be repeated in 
follow-up patches in the series, such as the changes in scm.c.

>  		if (!ssqd)
>  			return -ENOMEM;
>  	} else {
[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260916-s390-cio-ready-v3-0-39e4894637d6@kernel.org?part=12