RE: [Xen-devel] PV guest + shadow paging

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Sun, 2007-07-29 at 22:38 +0100, Ian Pratt wrote:
> > In a PV guest, shadow paging is used for logging dirty pages during
> > live
> > migration. For a HVM guest, it's enabled all the time due to full
> > virtualization.
> > 
> > Does the current version of Xen support running a PV guest with shadow
> > paging enabled all the time ? If so, will it work if I just put
> > "shadow_memory = 8"
> > in the cfg file ?
> 
> During live relocation of PV guests, shadow mode is used to log dirty
> page accesses, but its not used to do address translation. It is
> possible to get PV guests running in 'auto translate mode', but I'm 
> not sure it can be done via the guest config file. Since this mode is
> typically only used by various research projects its possible that
> support has rotted. Look for any references to auto translate mode in
> the domain builder for clues as to how to enable it.

Adding
        features = "auto_translated_physmap|writable_page_tables"
to the config file should add those features to the set passed to the
guest. I can't remember which set you would need to enable shadow mode,
you may have to dig round in the builder and/or hypervisor to figure it
out.

However I'm not sure shadow mode (other than log-dirty) isn't broken for
PV guests. It's been a long time since I tried it but it was broken back
when the paravirt_ops tree was still trying to use it.

Ian.


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