Re: [Xen-devel] ioreq server regression

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Paul Durrant
> Sent: 12 December 2016 16:29
> To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Boris Ostrovsky
> <boris.ostrovsky@xxxxxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Juergen
> Gross <jgross@xxxxxxxx>; xen-devel <xen-devel@xxxxxxxxxxxxx>
> Cc: zhangchen.fnst@xxxxxxxxxxxxxx
> Subject: RE: ioreq server regression
> 
> > -----Original Message-----
> > From: Andrew Cooper
> > Sent: 12 December 2016 16:27
> > To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Boris Ostrovsky
> > <boris.ostrovsky@xxxxxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Juergen
> > Gross <jgross@xxxxxxxx>; xen-devel <xen-devel@xxxxxxxxxxxxx>
> > Cc: zhangchen.fnst@xxxxxxxxxxxxxx
> > Subject: Re: ioreq server regression
> >
> > On 12/12/16 16:22, Paul Durrant wrote:
> > >> -----Original Message-----
> > >> From: Boris Ostrovsky [mailto:boris.ostrovsky@xxxxxxxxxx]
> > >> Sent: 12 December 2016 16:02
> > >> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Jan Beulich
> > >> <jbeulich@xxxxxxxx>; Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>;
> > >> Juergen Gross <jgross@xxxxxxxx>; xen-devel <xen-
> devel@xxxxxxxxxxxxx>
> > >> Cc: zhangchen.fnst@xxxxxxxxxxxxxx
> > >> Subject: ioreq server regression
> > >>
> > >> Looks like commit e7dabe59c ("x86/hvm: don't unconditionally create a
> > >> default ioreq server") breaks restore for HVM guests.
> > >>
> > >> I see "qemu: hardware error: Invalid ioreq type 0x53" in qemu log.
> > >>
> > > Damn, yes that will be the case when migrating with legacy QEMU...
> we're
> > going to need another flag that's set on the domain by the restore code so
> > that the default server also gets created on restore.
> >
> > I don't understand why the existing code doesn't suffice.  A domain
> > being restored is conceptually no different from one which is still
> > being constructed.
> >
> > The creation_finished flag should still be clear at this point during
> > restore.
> 
> That's the problem... The creation flag is clear so reading the HVM params
> does not instantiate the default ioreq server in the target domain.
> 

Sorry, ignore me... I my logic backwards.

I guess the creation flag must get set too early on restore.

  Paul

>   Paul
> 
> >  Is it perhaps something else doing a pause/unpause on the
> > domain before qemu starts up?  The creation_finished flag should only be
> > set at the first point the refcount goes to zero, not the first unpause
> > hypercall.
> >
> > ~Andrew
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