Re: [Xen-devel] Xen 4.1 + Linux compiled with PVH == BOOM

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-01-07 at 08:23 +0000, Jan Beulich wrote:
> >> that feature statically in the first place - that should be done only if 
> >> the 
> > kernel
> >> could _only_ boot in PVH mode.
> > 
> > The feature is not marked as "required" but rather - it can utilize said
> > extension (so supported). I am advocating that the calleer checks that
> > all of the required pieces are correct - and it can ignore the ones it
> > has no idea off (which it does for some of the Xen ELF notes - ignores
> > them if it has no idea of what they are).
> 
> What would be to point of telling the hypervisor that the kernel
> can utilize a certain extension? The kernel could just utilize it, and
> the hypervisor would know by that simple fact.

But for PVH doesn't the hypervisor need to now at dom0 build time
whether to build a PV or PVH domain? So it needs to know upfront if the
kernel could do PVH or not, and then pick, but once it has picked the
kernel had best follow that choice.

So in the PVH case it's not just a simple case of the kernel deciding to
utilize an optional feature, the optional feature has already been
enabled.

Ian


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