Re: [Qemu-devel] Re: LSI: avoid infinite loops

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, May 08, 2008 at 01:52:11AM +0100, Paul Brook wrote:
> On Thursday 08 May 2008, Paul Brook wrote:
> > On Thursday 08 May 2008, Marcelo Tosatti wrote:
> > > On Thu, May 08, 2008 at 12:21:54AM +0100, Paul Brook wrote:
> > > > On Thursday 08 May 2008, Marcelo Tosatti wrote:
> > > > > The Windows driver has SCRIPTS code which busy loops on main memory.
> > > > > So give the CPU's a chance to run if that happens.
> > > >
> > > > I'm kinda surprised this works.  What causes the scripts engine to be
> > > > restarted?
> > >
> > > LSI_ISTAT0_SIGP.
> >
> > In that case my surprise continues, and this is looking like an
> > unbelievably horrid hack.
> >
> > By my reading you're making LSI_ISTAT0_SIGP effect whatever instruction
> > happens to be executing when we stall. You get doubly lucky because (a) the
> > guest OS decides to bang on SIGP, even though it doesn't need to. And (b)
> > the last instruction executed happens to have set dnad to a value that
> > "works". I'm guessing you always happen to stop execution on the
> > conditional jump instruction and taking that jump doesn't cause any bad
> > effects, right?
> 
> Oh, I'd also be worried what happens if an async IO operation completes at 
> this point. lsi_command_complete is liable to trample all over your state.

So what do you suggest as a proper fix?