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Re: [PATCH] cpu: Add starts_halted() method

From: Peter Maydell
Subject: Re: [PATCH] cpu: Add starts_halted() method
Date: Wed, 8 Jul 2020 14:14:03 +0100

On Wed, 8 Jul 2020 at 12:12, David Gibson <david@gibson.dropbear.id.au> wrote:
> On Wed, Jul 08, 2020 at 10:38:29AM +0200, Philippe Mathieu-Daudé wrote:
> > Class boolean field certainly sounds better, but I am not sure this
> > is a property of the machine. Rather the arch? So move the field
> > to CPUClass? Maybe not, let's discuss :)
> It is absolutely a property of the machine.  e.g. I don't think we
> want this for powernv.  pseries is a bit of a special case since it is
> explicitly a paravirt platform.  But even for emulated hardware, the
> board can absolutely strap things so that cpus do or don't start
> immediately.

It's a property of the individual CPU, I think. One common setup
for Arm systems is that the primary CPU starts powered up but
the secondaries all start powered down.

The original bug as described in the commit message sounds
to me like something we should look to fix in the implementation
of async_run_on_cpu() -- it shouldn't cause a CPU that's halfway
through reset to do a KVM_RUN or otherwise run guest code,
whether that CPU is going to start powered-up or powered-down.

-- PMM

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