linux-kernel - Re: [PATCH] irqchip/gic-v3-its: Don't acquire rt_spin_lock in allocate_vpe_l1

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: <87pl7gglya.ffs@tglx>
Date: Sun, 11 Jan 2026 17:20:45 +0100
From: Thomas Gleixner <tglx@...nel.org>
To: Marc Zyngier <maz@...nel.org>
Cc: Waiman Long <longman@...hat.com>, Sebastian Andrzej Siewior
 <bigeasy@...utronix.de>, Clark Williams <clrkwllms@...nel.org>, Steven
 Rostedt <rostedt@...dmis.org>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH] irqchip/gic-v3-its: Don't acquire rt_spin_lock in
 allocate_vpe_l1_table()

On Sun, Jan 11 2026 at 10:38, Marc Zyngier wrote:
> On Sun, 11 Jan 2026 09:39:07 +0000,
> Thomas Gleixner <tglx@...nel.org> wrote:
>> 
>> On Fri, Jan 09 2026 at 16:13, Marc Zyngier wrote:
>> > On Thu, 08 Jan 2026 22:11:33 +0000,
>> > Thomas Gleixner <tglx@...nel.org> wrote:
>> >> At the point where a CPU is brought up, the topology should be known
>> >> already, which means this can be allocated on the control CPU _before_
>> >> the new CPU comes up, no?
>> >
>> > No. Each CPU finds *itself* in the forest of redistributors, and from
>> > there tries to find whether it has some shared resource with a CPU
>> > that has booted before it. That's because firmware is absolutely awful
>> > and can't present a consistent view of the system.
>> 
>> Groan....
>>
>> > Anyway, I expect it could be solved by moving this part of the init to
>> > an ONLINE HP callback.
>> 
>> Which needs to be before CPUHP_AP_IRQ_AFFINITY_ONLINE, but even that
>> might be to late because there are callbacks in the STARTING section,
>> i.e. timer, perf, which might rely on interrupts being accessible.
>
> Nah. This stuff is only for direct injection of vLPIs into guests, so
> as long as this is done before we can schedule a vcpu on this physical
> CPU, we're good. No physical interrupt is concerned with this code.

That's fine then. vCPUs are considered "user-space" tasks and can't be
scheduled before CPUHP_AP_ACTIVE sets the CPU active for the scheduler.

Thanks,

        tglx