Re: [Xen-devel] [RFC] ARM VM System Sepcification

[Christoffer Dall <christoffer.dall@xxxxxxxxxx>]

On Sat, Mar 22, 2014 at 09:08:37AM +0100, Paolo Bonzini wrote:
> Il 22/03/2014 03:29, Christoffer Dall ha scritto:
> >1. Simply mandate that VM implementations support persistent variables
> >   for their UEFI implementation - with whatever constraints that may
> >   put on higher level tools.
> >
> >2. Require that OSes shipped as part of compliant VM images make no
> >   assumption that changes to the UEFI environment will be stored.
> >
> >I feel that option number two will break in all sorts of cases, just
> >like Grant stated above, and it is fundamentally not practical; if a
> >distribution ships Linux with a UEFI stub that expects to be able to do
> >something, distributions must modify Linux to conform to this spec.  I
> >think imagining that this spec controls how UEFI support in Linux/Grub
> >is done in general would be overreaching.  Additionally, Michael brought
> >up the fact that it would be non-UEFI compliant.
> 
> OSes are already able to cope with loss of changes to UEFI
> environment are stored, because losing persistent variables is what
> happens if you copy an image to a new hard disk.
> 
> Asking implementations for support of persistent variables is a good
> idea; however, independent of what is in the spec, OSes should not
> expect that users will enable that support---most of them won't.
> 
OK, fair enough, mandating support for persistent variable storage may
be overreaching but at the same time I feel it is unlikely for this spec
to reach far enough that a generic UEFI Linux loader, for example,
actually follows it, and therefore explicitly mandating that guest OSes
must be completely portable in all that they do is a non-practical
constraint.  That was the request that kicked this discussion off, and
what I was trygint to address.

-Christoffer

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