Re: [Xen-devel] [PATCH v2 18/30] xen/x86: setup PVHv2 Dom0 ACPI tables

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 10/27/2016 10:30 AM, Jan Beulich wrote:
> > > > On 27.10.16 at 16:15, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > On 10/27/2016 10:02 AM, Jan Beulich wrote:
> > > > > > On 27.10.16 at 15:51, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > > > I re-read this thread and I am not sure I understand why we can't keep
> > > > host's RSDP descriptor. We are not mapping dom0 memory 1:1 (right?) so
> > > > we can place our versions of RSDT/XSDT at the address that the
> > > > descriptor points to.
> > > >
> > > > Unless that address is beyond dom0 memory allocation so that could be a
> > > > problem I guess.
> > > Also eventually we may want to add tables, not just remove some,
> > > and then there may not be enough space at the original location.
> > > Plus I think nothing precludes the XSDT living below 1Mb, and then
> > > we're back into the same problems discussed in another branch of
> > > this thread.
> > Yes, that is a problem.
> >
> > I guess we will need to do something in Linux to override descriptor
> > search. There is already some cruft for this but it appears to be
> > kexec-specific.
> As Roger pointed out - there should be kexec-independent logic
> to avoid that lookup on EFI systems (by finding the pointer earlier
> another way).

Yes, that's exactly what Linux does (acpi_os_get_root_pointer()) but 
that would imply that we are running on a UEFI system, which we are not. 
And trying to fake just this feature may cause other components to get 
confused.

-boris

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