Re: [Xen-devel] [PATCH] Fix hvm vcpu hotplug bug

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Liu, Jinsong writes ("[Xen-devel] [PATCH] Fix hvm vcpu hotplug bug"):
> When hotplug hvm vcpu by 'xm vcpu-set' command, if it add/remove
> many vcpus by 1 'xm vcpu-set' command, it has a bug that it cannot
> add/remove all vcpus that want to be added/removed.
> This patch is to fix the bug. It delays trigger sci until all xenstore
> cpu node status are watched.

This patch seems to arrange to take multiple CPU hot-add/remove events
and coalesce them into a single event.  It is obvious how this avoids
triggering a race, but I'm not convinced that it's a correct fix.

The core problem seems to be that somehow the SCI IRQ is lost ?
Perhaps the real problem is this code:
        qemu_set_irq(sci_irq, 1);
        qemu_set_irq(sci_irq, 0);

I'm not familiar with the way SCI is supposed to work but clearing the
irq in the qemu add/remove function seems wrong.  Surely the host
should clear the interrupt when it has serviced the interrupt.

Can you explain what I'm missing ?

Ian.

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