Re: [PATCH 26/32] s390/mm: Define KMSAN metadata for vmalloc and modules

[Alexander Potapenko]

On Wed, Nov 15, 2023 at 9:35 PM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> 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.
>
> 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..297c1062372a 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, PAGE_SIZE);
Is it okay that vmalloc_size is only aligned on PAGE_SIZE?
E.g. above the alignment is _REGION3_SIZE.