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

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

On Wed, Oct 26, 2016 at 01:14:16PM -0400, Boris Ostrovsky wrote:
> 
> >>>> I've initially used a back-listing approach. We can always change this 
> >>>> later 
> >>>> on.
> >>>>
> >>>> So I've ended up crafting a new MADT, XSDT and RSDP. Note that I'm not 
> >>>> crafting a new custom RSDT (and in fact I'm setting 
> >>>> rsdt_physical_address = 
> >>>> 0 in the RSDP together with revision = 2). This is all placed in RAM 
> >>>> stolen 
> >>>> from the guest memory map and marked as E820_ACPI, which means that the 
> >>>> new 
> >>>> RSDP no longer resides below 1MB, 
> 
> 
> As I mentioned in the other thread I am not sure this would be in
> compliance with the ACPI spec.

Right, the ACPI spec mandates that the RSDP must reside in the first 1 KB of 
the EBDA, or in the ROM regions between 0xE0000 0xFFFFF, but that's only 
when booted from a legacy BIOS, when booted from UEFI the RSDP can reside 
anywhere in memory, and the pointer must be fetched from a UEFI specific 
table. I would consider Xen to be similar to UEFI boot in that regard.

Roger.

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