Re: [PATCHv2] x86/xen: during early setup, only 1:1 map the ISA region

[David Vrabel <david.vrabel@citrix.com>]

On 25/07/13 16:46, Aurelien Chartier wrote:
> On 22/07/13 15:29, David Vrabel wrote:
>> From: David Vrabel <david.vrabel@citrix.com>
>>
>> During early setup, when the reserved regions and MMIO holes are being
>> setup as 1:1 in the p2m, clear any mappings instead of making them 1:1
>> (execept for the ISA region which is expected to be mapped).
>>
>> This fixes a regression introduced in 3.5 by 83d51ab473dd (xen/setup:
>> update VA mapping when releasing memory during setup) which caused
>> hosts with tboot to fail to boot.
>>
>> tboot marks a region in the e820 map as unusable and the dom0 kernel
>> would attempt to map this region and Xen does not permit unusable
>> regions to be mapped by guests.
>>
>> (XEN)  0000000000000000 - 0000000000060000 (usable)
>> (XEN)  0000000000060000 - 0000000000068000 (reserved)
>> (XEN)  0000000000068000 - 000000000009e000 (usable)
>> (XEN)  0000000000100000 - 0000000000800000 (usable)
>> (XEN)  0000000000800000 - 0000000000972000 (unusable)
>>
>> tboot marked this region as unusable.
>>
>> (XEN)  0000000000972000 - 00000000cf200000 (usable)
>> (XEN)  00000000cf200000 - 00000000cf38f000 (reserved)
>> (XEN)  00000000cf38f000 - 00000000cf3ce000 (ACPI data)
>> (XEN)  00000000cf3ce000 - 00000000d0000000 (reserved)
>> (XEN)  00000000e0000000 - 00000000f0000000 (reserved)
>> (XEN)  00000000fe000000 - 0000000100000000 (reserved)
>> (XEN)  0000000100000000 - 0000000630000000 (usable)
>>
>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
>> ---
>> v2: Extend 1:1 mapping region to cover 0 - 1MiB. find_ibft_region()
>> scans from 512 KiB and if this overlapped with a reserved region it
>> would crash.
> 
> I made more extensive testing and I was wrong, the crash I reported has
> been fixed upstream. I am able to boot a 3.11-rc1 kernel without any
> patch applied. However, I am still seeing errors in the log :
> 
> (XEN) mm.c:901:d0 Error getting mfn 800 (pfn 5555555555555555) from L1
> entry 0000000000800463 for l1e_owner=0, pg_owner=0
> 
> David's patch is fixing those errors.
> 
> I also tried applying that patch to 3.8.13.4, but dom0 was still
> crashing at boot time :

Does this
(http://lists.xen.org/archives/html/xen-devel/2013-07/msg00701.html)
patch work better?

I do think hiding UNUSABLE regions from dom0 is the right thing to do
and will be a more reliable fix going forwards, but Konrad didn't agree.

David