Re: [Xen-devel] Stubdom breakage in 4.5

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Don Slutz [mailto:dslutz@xxxxxxxxxxx]
> Sent: 04 February 2015 21:42
> To: Paul Durrant; Ian Campbell
> Cc: Wei Liu; Andrew Cooper; xen-devel@xxxxxxxxxxxxx; Stefano Stabellini; Jan
> Beulich; Ian Jackson
> Subject: Re: [Xen-devel] Stubdom breakage in 4.5
> 
> On 02/04/15 07:58, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Ian Campbell
> >> Sent: 04 February 2015 12:30
> >> To: Paul Durrant
> >> Cc: Wei Liu; xen-devel@xxxxxxxxxxxxx; Ian Jackson; Jan Beulich; Andrew
> >> Cooper; Stefano Stabellini
> >> Subject: Re: Stubdom breakage in 4.5
> >>
> >> On Tue, 2015-02-03 at 14:11 +0000, Paul Durrant wrote:
> >>> How about this as a slightly hacky solution that I think may work in both
> >> cases?
> >>>
> >>> If Xen finds no emulator at all for an HVM guest then it waits around
> >>> for at least one to show up before processing an emulation request.
> >>> Until one does it stalls the vcpu in question indefinitely, but on the
> >>> first emulator attach (i.e. ioreq server creations) then the IO will
> >>> always be processed, even if it doesn't match the ioreq server.
> >>
> >> It sounds plausible to me and seems like it would probably be
> >> backportable.
> >>
> >
> > Actually I think it may be even simpler, although I've not tried it. If
> hvm_domain_initialise() pauses the domain and the first
> hvm_ioreq_server_enable() unpauses it, I'm hoping that may be enough.
> >
> 
> You do need to keep the PVH case in mind here.

Yes indeed. My test patch does not do the extra pause for PVH.

Actually one thing that's in your patch series does 'help' a bit. The folding 
together of the has_dm check and the IO completion means that at least 
hvmloader gets back f-s rather than 0-s for the emulation that doesn't hit :-/

  Paul
 
>    -Don Slutz
> 
> 
> >> Longer term I think we still need to fix the domain creation interlock
> >> for launching multiple qemu's, ioreq servers and any other type of
> >> service thing we might launch (whether in a stub dom or not), at which
> >> point we may be able to remove the above workaround too.
> >>
> >
> > Yes. Once the toolstack is aware it can keep the domain paused until all
> emulators report readiness.
> >
> >   Paul
> >
> >> Ian.
> >>
> >>
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel
> >

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