Re: [Qemu-devel] [PATCH v2 1/6] Use IO port for qemu<->guest BIOS communication.

[Avi Kivity]

Blue Swirl wrote:
> > Put the lock in memory.  Or even simpler, have the boot cpu extract the
> >  parameters and place them in memory, and then wake up other cpus.
> >     
>
> Where in the memory?

Anywhere you like.  Of course that doesn't work if you need the 
information to get memory to work.

>  What about reset, when all CPUs are online? And
> CPUs would need to know if they are the boot CPU or not without
> disturbing our IO port.
>   

On x86, reset has once cpu running and the rest in a holding pattern.

If your arch has all cpus running on reset, and you can't determine 
which is cpu 0, you can construct a lock device using mmio which doesn't 
require any atomic ops.

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