Re: [Qemu-devel] [PATCH v4 05/11] suspend: add infrastructure

[Gleb Natapov]

On Tue, Feb 14, 2012 at 09:18:34AM +0100, Gerd Hoffmann wrote:
>   Hi,
> 
> > Shouldn't we stop the whole VM at some point, not only vcpu that
> > does ACPI IO? May be I missed where it is done in the patch series.
> 
> It isn't hidden elsewhere, qemu doesn't do it.   The code was like that
> before, and I think the reason is that the guest has to stop the other
> cpus before entering s3.
> 
Current code calls qemu_system_reset_request() which takes care of
stopping (and reseting) all vcpus (and rest of the machine) by setting
reset_requested flag immediately on suspend. We cannot just stop
current cpu on S3 and delay reset till wakeup since guest can leave
other vcpus in spinning state and they will take 100% of host cpu while
guest is suspended. I think it is also important to reset all device
immediately to ensure that no device will do DMA into main memory after
suspend. Technically if this happens it would be a guest bug since
guest should make sure that devices are stopped before entering S3,
but I wouldn't want to debug such bug report :)

--
                        Gleb.