Re: [PATCH v3 28/34] s390/mm: Define KMSAN metadata for vmalloc and modules

[Heiko Carstens]

On Thu, Dec 14, 2023 at 12:24:48AM +0100, Ilya Leoshkevich wrote:
> The pages for the KMSAN metadata associated with most kernel mappings
> are taken from memblock by the common code. However, vmalloc and module
> metadata needs to be defined by the architectures.
> 
> Be a little bit more careful than x86: allocate exactly MODULES_LEN
> for the module shadow and origins, and then take 2/3 of vmalloc for
> the vmalloc shadow and origins. This ensures that users passing small
> vmalloc= values on the command line do not cause module metadata
> collisions.
> 
> Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>
> Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> ---
>  arch/s390/boot/startup.c        |  8 ++++++++
>  arch/s390/include/asm/pgtable.h | 10 ++++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
> index 8104e0e3d188..e37e7ffda430 100644
> --- a/arch/s390/boot/startup.c
> +++ b/arch/s390/boot/startup.c
> @@ -253,9 +253,17 @@ static unsigned long setup_kernel_memory_layout(void)
>  	MODULES_END = round_down(__abs_lowcore, _SEGMENT_SIZE);
>  	MODULES_VADDR = MODULES_END - MODULES_LEN;
>  	VMALLOC_END = MODULES_VADDR;
> +#ifdef CONFIG_KMSAN
> +	VMALLOC_END -= MODULES_LEN * 2;
> +#endif
>  
>  	/* allow vmalloc area to occupy up to about 1/2 of the rest virtual space left */
>  	vmalloc_size = min(vmalloc_size, round_down(VMALLOC_END / 2, _REGION3_SIZE));
> +#ifdef CONFIG_KMSAN
> +	/* take 2/3 of vmalloc area for KMSAN shadow and origins */
> +	vmalloc_size = round_down(vmalloc_size / 3, _REGION3_SIZE);
> +	VMALLOC_END -= vmalloc_size * 2;
> +#endif

Please use

	if (IS_ENABLED(CONFIG_KMSAN))

above, since this way we get more compile time checks.

> +#ifdef CONFIG_KMSAN
> +#define KMSAN_VMALLOC_SIZE (VMALLOC_END - VMALLOC_START)
> +#define KMSAN_VMALLOC_SHADOW_START VMALLOC_END
> +#define KMSAN_VMALLOC_ORIGIN_START (KMSAN_VMALLOC_SHADOW_START + \
> +				    KMSAN_VMALLOC_SIZE)
> +#define KMSAN_MODULES_SHADOW_START (KMSAN_VMALLOC_ORIGIN_START + \
> +				    KMSAN_VMALLOC_SIZE)

Long single lines for these, please :)

With that, and Alexander Gordeev's comments addressed:
Acked-by: Heiko Carstens <hca@xxxxxxxxxxxxx>