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    SubjectRe: [PATCH v3 28/34] s390/mm: Define KMSAN metadata for vmalloc and modules
    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@google.com>
    > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
    > ---
    > 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));

    Since commit 2a65c6e1ad06 ("s390/boot: always align vmalloc area on segment boundary")
    vmalloc_size is aligned on _SEGMENT_SIZE boundary.

    > +#ifdef CONFIG_KMSAN
    > + /* take 2/3 of vmalloc area for KMSAN shadow and origins */
    > + vmalloc_size = round_down(vmalloc_size / 3, _REGION3_SIZE);

    And thus, the alignment here should be _SEGMENT_SIZE as well.

    > + VMALLOC_END -= vmalloc_size * 2;
    > +#endif
    > VMALLOC_START = VMALLOC_END - vmalloc_size;
    >
    > /* split remaining virtual space between 1:1 mapping & vmemmap array */

    ...

    With the above fixup:
    Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>

    Thanks!

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