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

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

On Thu, Oct 27, 2016 at 10:40:52AM -0400, Boris Ostrovsky wrote:
> 
> 
> 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.

TBH, I would just make acpi_rsdp not dependent on KEXEC, but is this going 
to be propagated to user-space tools somehow (ie: so that acpidump will 
report the right tables)?

I prefer this solution because it seems simpler and less likely to cause 
future issues, but if this seems like too much fuss I can always try to 
place the RSDP on top of the original one and shadow that page. From the 
information I've been able to find on the Internet, the EBDA just seems to 
contain the position of the pointing device (PS/2 mouse) [0], which I doubt 
is used by any modern OS.

Roger.

[0] 
http://www.msc-technologies.eu/fileadmin/documentpool/Support-Center/Archive/70-PISA/PISA-P/02-Manual/BIOS%20Programmer's%20Guide%20v10.pdf?file=&ref=

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel