[Qemu-ppc] pseries on qemu-system-ppc64le crashes in doorbell_core_ipi()

[Jason A. Donenfeld]

On Thu, Dec 19, 2019 at 12:13 PM Sebastian Andrzej Siewior
<bigeasy at linutronix.de> wrote:
> Based on my understanding is that the doorbell feature is part of the
> architecture. It can be used to signal other siblings on the same CPU.
> qemu TCG doesn't support that and does not allow to announce multiple
> siblings on the same CPU. However, the kernel uses this interface if it
> tries to send an interrupt to itself (the same CPU) so everything
> matches.
> Last time I run into this, the interface was change so the kernel das
> not send an IPI to itself. This changed now for another function…

One way of fixing this is to just "not use the feature", as you seem
to be suggesting.

But actually shouldn't there be some CPU feature detection available?
Something like -- QEMU advertises to the kernel that it supports or
doesn't support doorbells, and the kernel then avoids those paths if
the CPU feature flag isn't present?

Jason