[PATCH v2 0/2] fix wrong usage of memory allocation APIs under PREEMPT_RT in arm64

[Yeoreum Yun]

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


 arch/arm64/mm/mmu.c | 235 ++++++++++++++++++++++++++++++++++----------
 1 file changed, 183 insertions(+), 52 deletions(-)

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