linux-kernel - Re: [PATCH v3 0/2] fix wrong usage of memory allocation APIs under PREEMPT

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Message-ID: <aVT15bhN4hEBNaOg@e129823.arm.com>
Date: Wed, 31 Dec 2025 10:07:33 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: catalin.marinas@....com, will@...nel.org, ryan.roberts@....com,
	akpm@...ux-foundation.org, david@...nel.org, kevin.brodsky@....com,
	quic_zhenhuah@...cinc.com, dev.jain@....com,
	yang@...amperecomputing.com, chaitanyas.prakash@....com,
	bigeasy@...utronix.de, clrkwllms@...nel.org, rostedt@...dmis.org,
	lorenzo.stoakes@...cle.com, ardb@...nel.org, jackmanb@...gle.com,
	vbabka@...e.cz, mhocko@...e.com
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH v3 0/2]  fix wrong usage of memory allocation APIs under
 PREEMPT_RT in arm64

Gentle ping in case of forgotten.

On Thu, Dec 18, 2025 at 07:47:48PM +0000, Yeoreum Yun wrote:
> 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 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/
>
>
> *** BLURB HERE ***
>
> Yeoreum Yun (2):
>   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 | 254 ++++++++++++++++++++++++++++++++++----------
>  1 file changed, 197 insertions(+), 57 deletions(-)
>
> --
> LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
>

--
Sincerely,
Yeoreum Yun