On Mon, 12 Jan 2026 11:20:07 +0000,
Marc Zyngier [off-list ref] wrote:

On Sun, 11 Jan 2026 16:20:45 +0000,
Thomas Gleixner [off-list ref] wrote:

quoted

On Sun, Jan 11 2026 at 10:38, Marc Zyngier wrote:

quoted

On Sun, 11 Jan 2026 09:39:07 +0000,
Thomas Gleixner [off-list ref] wrote:

quoted

On Fri, Jan 09 2026 at 16:13, Marc Zyngier wrote:

quoted

On Thu, 08 Jan 2026 22:11:33 +0000,
Thomas Gleixner [off-list ref] wrote:

quoted

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....

quoted

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.

Waiman, can you please give the following hack a go on your box? The
machines I have are thankfully limited to a single ITS group, so I
can't directly reproduce your issue.

Have you managed to try this hack? I may be able to spend some time
addressing the issue in the next cycle if I have an indication that
I'm on the right track.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.