On 21/08/26 17:04, Pratyush Yadav wrote:
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.
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.
Cc: Aditya Gupta <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Christophe Leroy (CS GROUP) <[email protected]>
Cc: Hari Bathini <[email protected]>
Cc: Madhavan Srinivasan <[email protected]>
Cc: Mahesh Salgaonkar <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Pasha Tatashin <[email protected]>
Cc: Pratyush Yadav <[email protected]>
Cc: Ritesh Harjani (IBM) <[email protected]>
Cc: Shivang Upadhyay <[email protected]>
Cc: Shrikanth Hegde <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Sourabh Jain <[email protected]>
---
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
