Re: [RFC PATCH 3/3] powerpc/kho: exclude THP and HUGETLB_PAGE

On Fri, Aug 21 2026, Sourabh Jain wrote:

Enabling CONFIG_KEXEC_HANDOVER together with CONFIG_TRANSPARENT_HUGEPAGE
or CONFIG_HUGETLB_PAGE on powerpc fails to build:

    kernel/liveupdate/kexec_handover.c:49:39: error: expression in static assertion is not constant
       49 | static_assert(SCRATCH_ALIGNMENT_BYTES >= CMA_MIN_ALIGNMENT_BYTES);
    ./include/linux/build_bug.h:80:56: note: in definition of macro '__static_assert'
       80 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
          |                                                        ^~~~
    kernel/liveupdate/kexec_handover.c:49:1: note: in expansion of macro 'static_assert'
       49 | static_assert(SCRATCH_ALIGNMENT_BYTES >= CMA_MIN_ALIGNMENT_BYTES);

CMA_MIN_ALIGNMENT_BYTES is derived from pageblock_order, which on
powerpc is not a compile-time constant when THP or HUGETLB_PAGE is
enabled -- powerpc can determine huge page size at runtime in that
configuration, so pageblock_order becomes a variable rather than a
constant expression. KHO's static_assert() on
SCRATCH_ALIGNMENT_BYTES >= CMA_MIN_ALIGNMENT_BYTES then fails to
compile, since it requires both sides to be constant expressions.

Until CMA_MIN_ALIGNMENT_BYTES (or KHO's use of it) is made to handle
the non-constant pageblock_order case on powerpc, exclude
TRANSPARENT_HUGEPAGE and HUGETLB_PAGE from ARCH_SUPPORTS_KEXEC_HANDOVER
so the two can't be enabled together and hit this build failure.

This should be a part of patch 2 I think. It is not a good idea to break
the build in one patch and fix it in the next.

That said, this is a debug check of sorts since SCRATCH_ALIGNMENT_BYTES
is of MAX_ORDER_NR_PAGES, and pageblocks _should_ always be smaller of
equal to this.

Anyway, I don't think this is something you should gate by a config. I
think you should either remove the static_assert(), or turn it into a
runtime check.

+Cc Michal.

-- 
Regards,
Pratyush Yadav