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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 10/27/2016 11:04 AM, Roger Pau Monne wrote:
> 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)?

(Sorry, I forgot to respond)

If a tool is reading /sys/firmware/acpi/tables then I think it will see
what the kernel is using. acpidump, for example, *is* reading this
directory.

-boris

>
> 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