[PATCH 0/2] introduce pagetable_alloc_nolock()

Yeoreum Yun
2025-12-12T16:18:40Z

Some architectures invoke pagetable_alloc() or __get_free_pages()
with preemption disabled.
For example, in arm64, linear_map_split_to_ptes() calls pagetable_alloc()
while spliting block entry to ptes and __kpti_install_ng_mappings()
calls __get_free_pages() to create kpti pagetable.

Under PREEMPT_RT, calling pagetable_alloc() with
preemption disabled is not allowed, because it may acquire
a spin lock that becomes sleepable on RT, potentially
causing a sleep during page allocation.

Since above two functions is called as callback of stop_machine()
where its callback is called in preemption disabled,
They could make a potential problem. (sleeping in preemption disabled).

To address this, introduce pagetable_alloc_nolock() API.

Yeoreum Yun (2):
mm: introduce pagetable_alloc_nolock()
arm64: mmu: use pagetable_alloc_nolock() while stop_machine()

arch/arm64/mm/mmu.c | 23 ++++++++++++++++++-----
include/linux/mm.h | 18 ++++++++++++++++++
kernel/bpf/stream.c | 2 +-
kernel/bpf/syscall.c | 2 +-
mm/page_alloc.c | 10 +++-------
5 files changed, 41 insertions(+), 14 deletions(-)

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