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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
>On 25/07/13 16:46, Aurelien Chartier wrote:
>> On 22/07/13 15:29, David Vrabel wrote:
>>> From: David Vrabel <david.vrabel@xxxxxxxxxx>
>>>
>>> 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@xxxxxxxxxx>
>>> ---
>>> 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

It well might but we need to:
 -  Know why it is still happening after a fix that is tailored towards the fix 
and still does not work with stable kernels.  What are we missing? 
 -  it is unclear to me how this will affect PV DomU with PCI pass through 
which use  e820_hole parameter -  which means that the e820 in the guest is 
similar to the host one. We can't break them. 

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