Re: [Xen-devel] ioreq server regression

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----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.

  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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