Re: Xen, ACPI and Linux

[Ian Campbell <ian.campbell@citrix.com>]

On Wed, 2015-09-23 at 01:18 -0700, Ard Biesheuvel wrote:
> On 23 September 2015 at 01:12, Jan Beulich <JBeulich@suse.com> wrote:
> > > > > On 23.09.15 at 02:49, <stefano.stabellini@eu.citrix.com> wrote:
> > > Regarding Runtime Services, the EFI spec doesn't allow a NULL pointer
> > > to
> > > the Runtime Services table, so Mark would like to see a proper
> > > pointer
> > > being passed there.  The function table could be populated with
> > > hypercall wrappers in assembly, keeping the same interface to Xen
> > > that
> > > we have today in drivers/xen/efi.c. It should be part of the initial
> > > patch series.
> > 
> > I'm confused by the "interface to Xen" part: Aren't we talking about
> > what is being presented to Dom0?
> > 
> 
> Yes we are.
> 
> > In any event, the versioning question that I raised earlier remains:
> > Which version would you intend the Runtime Services table to carry
> > - the host one, or a Xen set one? In the latter case, won't you risk
> > wrong implications from the kernel looking at other version numbers
> > (yes, with proper coding it ought to be possible to avoid such, but
> > the multitude of version numbers in EFI doesn't exactly help to
> > avoid mistakes)? While in the former case you'd have to deal with
> > the table needing entries Xen may not know about.
> > 
> 
> This is simply addressed by populating the fake EFI system table
> according to the UEFI spec version field that you put in the header.
> No reason at all to base this on whatever the host provides, it should
> simply be a version that is supported by arm64 (2.00 or greater)

This doesn't address Jan's concern wrt the multiple other places UEFI
exposes version numbers which may reflect the host and not this fake EFI
table.

Ian.