Re: [Xen-devel] [PATCH for 4.6 v2 3/3] xl/libxl: disallow saving a guest with vNUMA configured

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Sep 09, 2015 at 01:33:15PM -0400, Boris Ostrovsky wrote:
> On 09/09/2015 01:29 PM, Wei Liu wrote:
> >On Wed, Sep 09, 2015 at 01:17:40PM -0400, Boris Ostrovsky wrote:
> >>On 09/09/2015 01:03 PM, Wei Liu wrote:
> >>>This is due to migration v2 frame record doesn't contain node
> >>>information.
> >>>
> >>>Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> >>>---
> >>>Cc: andrew.cooper3@xxxxxxxxxx
> >>>---
> >>>  docs/man/xl.cfg.pod.5   |  2 ++
> >>>  tools/libxl/libxl_dom.c | 14 ++++++++++++++
> >>>  2 files changed, 16 insertions(+)
> >>>
> >>>diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
> >>>index 80e51bb..dbd0700 100644
> >>>--- a/docs/man/xl.cfg.pod.5
> >>>+++ b/docs/man/xl.cfg.pod.5
> >>>@@ -263,6 +263,8 @@ virtual node.
> >>>  Note that virtual NUMA for PV guest is not yet supported, because
> >>>  there is an issue with cpuid handling that affects PV virtual NUMA.
> >>>+Further more, guest with virtual NUMA cannot be saved or migrated
> >>>+because node information of guest frames is not preserved.
> >>Should we also issue a warning during startup if nomigrate is not set?
> >>
> ><dig dig>
> >
> >Ah, there is such option. I can certainly give a warning. The only
> >problem is it seems to be stale in libxl, there is no code that checks
> >that! I can still migrate a guest even with nomigrate set to true.
> >
> >Maybe someone with more knowledge about that option can lecture me on
> >what that does? The manpage says it *enables* certain feature? Does that
> >actually mean *make available*?
> 
> IIRC it was added to allow/control certain TSC modes (see domain_cpuid()).
> 

To the best of my knowledge the nomigrate option is both semantically
and functionally broken.

I'm not very inclined to print a warning because setting that option
won't provide any protection / added value.

Wei.

> -boris
> 

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