Re: [PATCH] irqchip/gic-v3-its: Don't acquire rt_spin_lock in allocate_vpe_l1_table()

[Thomas Gleixner <tglx@kernel.org>]

On Sun, Jan 11 2026 at 10:38, Marc Zyngier wrote:
> On Sun, 11 Jan 2026 09:39:07 +0000,
> Thomas Gleixner <tglx@kernel.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@kernel.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