Re: Fresh install of Windows XP hangs early in boot?

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Jul 29, 2008 at 03:00:06PM -0700, Roland Dreier wrote:
>  > Known problem:
>  > http://www.nabble.com/LSI:-avoid-infinite-loops-p17116605.html
> 
>  > Windows driver has scripts code which busy loops on main memory. Since
>  > that executes in vcpu context, the cpu won't ever get a chance to change
>  > the variable which the SCSI emulation is looping at.
> 
> Thanks Marcelo (and Alberto) for pointing me at this.
> 
>  > The proposed hack, however, is half-assed (see Paul Brook's comments on
>  > that thread).
> 
> I'd be willing to take a stab at a better fix.  

Awesome! That would be very welcome. It is quite important for
better-than-IDE performance with Windows guests.

> Is there any documentation about the lsi microcode engine anywhere?

http://www.lsi.com/files/docs/techdocs/storage_stand_prod/SCSIControllers/56_3.pdf

> Would the right fix to be to detect the busy loop on CPU memory and
> return from lsi_execute_script() in that case?

Detect the busy loop, interrupt script execution but guaranteeing that
it will continue (by starting a timer to restart execution some time in
the future, for example).

The tricky part is that in between, SCRIPTS execution could have been
restarted by the guest via PIO/MMIO, or by an I/O completion event, so 
proper synchronization is needed.

The hack I did relied on the driver to restart execution by Signal
Process command (SIGP), but its possible that such command would never
be sent (as Paul Brook mentions in the thread).

> BTW I tried using if=ide to install Windows XP and got a blue screen
> during the installer.  What are people doing to run XP in a kvm guest?

Are you using a recent version of kvm-userspace/kernel modules? Please
save the blue screen and mail it to the list or fill a bug.

Thanks