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

On 21/08/26 17:04, Pratyush Yadav wrote:

On Fri, Aug 21 2026, Sourabh Jain wrote:

quoted

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.

Agree. Since this is an RFC patch series, I kept it separate so that this issue could
be reviewed independently from patch 2. Going forward, I will merge them.

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.

Agreed. I will evaluate both options and decide which approach makes more sense.

Thanks for the review Pratyush.

- Sourabh Jain

+Cc Michal.

quoted

Cc: Aditya Gupta <redacted>
Cc: Alexander Graf <graf@amazon.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Shivang Upadhyay <redacted>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: kexec@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Sourabh Jain <redacted>
---
  arch/powerpc/Kconfig | 1 +
  1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 61350d3e7a19..f68b9fc883ba 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig

@@ -720,6 +720,7 @@ config ARCH_SUPPORTS_KEXEC_HANDOVER
  	def_bool y
  	depends on PPC64
  	depends on !CRASH_DUMP
+	depends on !TRANSPARENT_HUGEPAGE && !HUGETLB_PAGE
  
  config ARCH_SUPPORTS_CRASH_HOTPLUG
  	def_bool y