Re: [Xen-devel] live migrating hvm from 4.4 to 4.7 fails in ioreq server

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, May 11, 2016 at 12:38:46PM +0000, Paul Durrant wrote:
> > -----Original Message-----
> > From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> > Sent: 11 May 2016 13:23
> > To: Olaf Hering; xen-devel@xxxxxxxxxxxxx; Paul Durrant
> > Subject: Re: [Xen-devel] live migrating hvm from 4.4 to 4.7 fails in ioreq
> > server
> > 
> > On 11/05/16 13:18, Olaf Hering wrote:
> > > Migrating a HVM guest from staging-4.4 to staging fails:
> > >
> > > # cat /var/log/xen/qemu-dm-fv-x64-sles12sp1-clean--incoming.log
> > > char device redirected to /dev/pts/3 (label serial0)
> > > xen: ioreq server create: Cannot allocate memory
> > > qemu-system-x86_64: xen hardware virtual machine initialisation failed
> > >
> > > Looks like hvm_alloc_ioreq_gmfn finds no bit in
> > > d->arch.hvm_domain.ioreq_gmfn.mask.  Is there a slim change that 4.4
> > does not
> > > know about HVM_PARAM_NR_IOREQ_SERVER_PAGES, and as a result 4.7
> > fails to
> > > configure the guest properly?
> > 
> > HVM_PARAM_NR_IOREQ_SERVER_PAGES was introduced in 4.6 iirc.  CC'ing
> > Paul
> > who did this work.
> 
> The problem is because the new QEMU will assume that the guest was 
> provisioned with ioreq server pages. Somehow it needs to know to behave as a 
> 'default' ioreq server (as qemu trad would) in which case the compatibility 
> code in the hypervisor would DTRT. I guess it would be ok to just have QEMU 
> fall back to the old 'default' HVM param mechanism if creation of an IOREQ 
> server fails. The only other way out would be allow Xen to 'steal' the 
> default server's pages if it doesn't exist.
> The former obviously requires a patch to QEMU (but the compat code already 
> exists as a compile-time option so it's probably a small-ish change) and the 
> latter requires a patch to Xen. Which is more preferable at this stage?
> 

Please help me understand: both ways require patching latest xen.git or
qemu.git, not patching xen 4.4 or the qemu shipped in 4.4. Right?

Wei.

>   Paul
> 
> > 
> > ~Andrew
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