Re: [Xen-devel] Regression in OSSTest Windows install test case

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> Sent: 16 July 2015 10:03
> To: Paul Durrant
> Cc: Wei Liu; xen-devel@xxxxxxxxxxxxxxxxxxxx; Jan Beulich; Andrew Cooper
> Subject: Re: Regression in OSSTest Windows install test case
> 
> On Thu, Jul 16, 2015 at 09:39:42AM +0100, Paul Durrant wrote:
> [...]
> > I think I found the semantic difference. Prior to this patch it would seem
> that stdvga buffered writes even when not in stdvga mode. When I tested
> your config (using cirrus), windows drops out of stdvga quite early in boot
> which slows down the splash screen to a crawl. When I just uncommented
> the single line 'stdvga=1' then I got through the splash screen several orders
> of magnitude faster.
> > So, I think this (compile tested only) incremental patch should fix the 
> > test:
> >
> > diff --git a/xen/arch/x86/hvm/stdvga.c b/xen/arch/x86/hvm/stdvga.c
> > index 6d22b22..d528155 100644
> > --- a/xen/arch/x86/hvm/stdvga.c
> > +++ b/xen/arch/x86/hvm/stdvga.c
> > @@ -441,7 +441,7 @@ static int stdvga_mem_write(const struct
> hvm_io_handler *han
> >      };
> >      struct hvm_ioreq_server *srv;
> >
> > -    if ( !s->cache )
> > +    if ( !s->cache || !s->stdvga )
> >          goto done;
> >
> >      /* Intercept mmio write */
> > @@ -503,9 +503,6 @@ static bool_t stdvga_mem_accept(const struct
> hvm_io_handler
> >
> >      spin_lock(&s->lock);
> >
> > -    if ( !s->stdvga )
> > -        goto reject;
> > -
> >      if ( p->dir == IOREQ_WRITE && p->count > 1 )
> >      {
> >          /*
> > @@ -526,7 +523,7 @@ static bool_t stdvga_mem_accept(const struct
> hvm_io_handler
> >
> >          goto reject;
> >      }
> > -    else if ( p->dir == IOREQ_READ && !s->cache )
> > +    else if ( p->dir == IOREQ_READ && !s->cache && !s->stdvga )
> >          goto reject;
> >
> >      /* s->lock intentionally held */
> >
> > I can't say that I like the idea of unconditionally buffering VRAM writes, 
> > but
> I'll test patch and post it.
> >
> 
> Thank you for the fix. It fixes the problem for me.

Cool. There's actually a small bug-ette in it. The line:

else if ( p->dir == IOREQ_READ && !s->cache && !s->stdvga )

should be:

else if ( p->dir == IOREQ_READ && (!s->cache || !s->stdvga) )

I don't think that will affect the behaviour in this case though since I very 
much doubt Windows is reading VRAM at this stage. Could you perhaps re-test 
with that change?

Cheers,

  Paul

> 
> Tested-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> 
> >   Paul
> >
> >
> 
> 
> 
> > > Wei.

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