Re: [PATCH v5 36/37] s390/kmsan: Implement the architecture-specific functions

Alexander Gordeev
2024-06-20T09:25:45Z

On Wed, Jun 19, 2024 at 05:44:11PM +0200, Ilya Leoshkevich wrote:

Hi Ilya,

> +static inline bool is_lowcore_addr(void *addr)
> +{
> + return addr >= (void *)&S390_lowcore &&
> + addr < (void *)(&S390_lowcore + 1);
> +}
> +
> +static inline void *arch_kmsan_get_meta_or_null(void *addr, bool is_origin)
> +{
> + if (is_lowcore_addr(addr)) {
> + /*
> + * Different lowcores accessed via S390_lowcore are described
> + * by the same struct page. Resolve the prefix manually in
> + * order to get a distinct struct page.
> + */

> + addr += (void *)lowcore_ptr[raw_smp_processor_id()] -
> + (void *)&S390_lowcore;

If I am not mistaken neither raw_smp_processor_id() itself, nor
lowcore_ptr[raw_smp_processor_id()] are atomic. Should the preemption
be disabled while the addr is calculated?

But then the question arises - how meaningful the returned value is?
AFAICT kmsan_get_metadata() is called from a preemptable context.
So if the CPU is changed - how useful the previous CPU lowcore meta is?

Is it a memory block that needs to be ignored instead?

> + if (WARN_ON_ONCE(is_lowcore_addr(addr)))
> + return NULL;

lowcore_ptr[] pointing into S390_lowcore is rather a bug.

> + return kmsan_get_metadata(addr, is_origin);
> + }
> + return NULL;
> +}

Thanks!