[PATCH v5 0/3] fix wrong usage of memory allocation APIs under PREEMPT_RT in arm64

Yeoreum Yun
2026-01-05T20:23:33Z

Under PREEMPT_RT, calling generic memory allocation/free APIs
(e.x) __get_free_pages(), pgtable_alloc(), free_pages() and etc
with preemption disabled is not allowed, but allow only nolock() APIs series
because it may acquire a spin lock that becomes sleepable on RT,
potentially causing a sleep during page allocation
(See Documentation/core-api/real-time/differences.rst, Memory allocation section).

However, In arm64, __linear_map_split_to_ptes() and
__kpti_install_ng_mappings() called by stopper thread via stop_machine()
use generic memory allocation/free APIs.

This patchset fixes this problem and based on v6.19-rc1

Patch History
==============
from v4 to v5:
- rebase to v6.19-rc4
- remove useless __always_inline
- fix alignments
- https://lore.kernel.org/all/20260102150736.1378818-1-yeoreum.yun@arm.com/

from v3 to v4:
- rebase to v6.19-rc3
- introduce pgtable_alloc_t
- following several suggestions from @Ryan Roberts
- https://lore.kernel.org/all/20251218194750.395301-1-yeoreum.yun@arm.com/

from v2 to v3:
- remove split-mode and split_args.
pass proper function pointer while spliting.
- rename function name.
- https://lore.kernel.org/all/20251217182007.2345700-1-yeoreum.yun@arm.com/

from v1 to v2:
- drop pagetable_alloc_nolock()
- following @Ryan Roberts suggestion.
- https://lore.kernel.org/all/20251212161832.2067134-1-yeoreum.yun@arm.com/

Yeoreum Yun (3):
arm64: mmu: introduce pgtable_alloc_t
arm64: mmu: avoid allocating pages while splitting the linear mapping
arm64: mmu: avoid allocating pages while installing ng-mapping for
KPTI

arch/arm64/mm/mmu.c | 241 ++++++++++++++++++++++++++++++++++----------
1 file changed, 186 insertions(+), 55 deletions(-)

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