Re: [PATCH for-4.10] libxc: load acpi RSDP table at correct address

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 20/11/2017 09:55, Juergen Gross wrote:
> On 20/11/17 10:51, Roger Pau Monné wrote:
>> Adding xen-devel, dropped it on my reply. 
>>
>>     Replying from my phone, sorry for the formatting. 
>>
>>
>>     El 20 nov. 2017 9:35, "Juergen Gross" <jgross@suse.com
>>     <mailto:jgross@suse.com>> escribió:
>>
>>         For PVH domains loading of the ACPI RSDP table is done via
>>         allocating
>>         a domain loader segment after having loaded the kernel. This
>>         leads to
>>         the RSDP table being loaded at an arbitrary guest address instead of
>>         the architectural correct address just below 1MB. 
>>
>>
>>     AFAIK this is only true for legacy BIOS boot, when using UEFI the
>>     RSDP can be anywhere in memory, hence grub2 must already have an
>>     alternative way of finding the RSDP apart from scanning the low 1MB.
> The problem isn't grub2, but the loaded linux kernel. Without this
> patch Linux won't find the RSDP when booted in a PVH domain via grub2.
>
> I could modify grub2 even further to move the RSDP to the correct
> address, but I think doing it correctly on Xen side is the better
> option.

Why?  The PVH info block contains a pointer directly to the RSDP, and
Linux should be following this rather than scanning for it using the
legacy method.

~Andrew

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