linux-kernel - Re: [PATCH 2/2] arm64: mmu: use pagetable_alloc_nolock() while stop

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aUPJuZINNuNxddRX@tiehlicka>
Date: Thu, 18 Dec 2025 10:30:33 +0100
From: Michal Hocko <mhocko@...e.com>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: akpm@...ux-foundation.org, david@...nel.org, lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com, vbabka@...e.cz, rppt@...nel.org,
	surenb@...gle.com, ast@...nel.org, daniel@...earbox.net,
	andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com,
	song@...nel.org, yonghong.song@...ux.dev, john.fastabend@...il.com,
	kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com,
	jolsa@...nel.org, jackmanb@...gle.com, hannes@...xchg.org,
	ziy@...dia.com, bigeasy@...utronix.de, clrkwllms@...nel.org,
	rostedt@...dmis.org, catalin.marinas@....com, will@...nel.org,
	ryan.roberts@....com, kevin.brodsky@....com, dev.jain@....com,
	yang@...amperecomputing.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] arm64: mmu: use pagetable_alloc_nolock() while
 stop_machine()

On Fri 12-12-25 16:18:32, Yeoreum Yun wrote:
> linear_map_split_to_ptes() and __kpti_install_ng_mappings()
> are called as callback of stop_machine().
> That means these functions context are preemption disabled.
> 
> Unfortunately, under PREEMPT_RT, the pagetable_alloc() or
> __get_free_pages() couldn't be called in this context
> since spin lock that becomes sleepable on RT,
> potentially causing a sleep during page allocation.
> 
> To address this, pagetable_alloc_nolock().

As you cannot tolerate allocation failure and this is pretty much
permanent allocation (AFAIU) why don't you use a static allocation?

-- 
Michal Hocko
SUSE Labs