Re: [PATCH] target/i386: introduce CPU property to work around Windows reset bug

[Daniel P . Berrangé]

On Thu, Mar 24, 2022 at 06:13:03PM +0100, Paolo Bonzini wrote:
> On 3/24/22 12:24, Paolo Bonzini wrote:
> > That said, the VMware kbase does paint a slightly different picture.  It
> > implies that starting with hardware version 11 rebooting Windows is done
> > through a hard reset instead of INIT.  I'm not sure how that would be
> > done, but in the meanwhile our fix should take care of do_cpu_init as
> > well.
> 
> Ok, so here are my findings:
> 
> - Windows resets the system by writing 0xFE to port 0x64.  This is a hard
> reset on QEMU, but presumably it was a soft reset (INIT) on VMware until
> version 10.
> 
> - QEMU _does_ try to write 0 to the TSC on hard reset.  But KVM special
> cases 0 as "somebody is trying to hot-plug a new CPU" and wants to help out,
> so it keeps the CPU synchronized with the previous TSC.
> 
> So this is a pretty clear-cut QEMU bug.  It can be fixed by e.g. writing 1
> to the TSC instead of 0.

Ah, excellant findings, so we won't need a config knob after all.

With regards,
Daniel
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