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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 19 Dec 2019 12:19:14 +0100
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Subject: Re: [Qemu-ppc] pseries on qemu-system-ppc64le crashes in
 doorbell_core_ipi()
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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On Thu, Dec 19, 2019 at 12:13 PM Sebastian Andrzej Siewior
<bigeasy@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=E2=80=A6

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