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Re: HVM/PVH Balloon crash

  • To: Elliott Mitchell <ehem+xen@xxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 15 Sep 2021 08:05:05 +0200
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  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 15 Sep 2021 06:05:25 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 15.09.2021 04:40, Elliott Mitchell wrote:
> On Tue, Sep 07, 2021 at 05:57:10PM +0200, Jan Beulich wrote:
>> On 07.09.2021 17:03, Elliott Mitchell wrote:
>>>  Could be this system is in an
>>> intergenerational hole, and some spot in the PVH/HVM code makes an
>>> assumption of the presence of NPT guarantees presence of an operational
>>> IOMMU.  Otherwise if there was some copy and paste while writing IOMMU
>>> code, some portion of the IOMMU code might be checking for presence of
>>> NPT instead of presence of IOMMU.
>> This is all very speculative; I consider what you suspect not very likely,
>> but also not entirely impossible. This is not the least because for a
>> long time we've been running without shared page tables on AMD.
>> I'm afraid without technical data and without knowing how to repro, I
>> don't see a way forward here.
> Downtimes are very expensive even for lower-end servers.  Plus there is
> the issue the system wasn't meant for development and thus never had
> appropriate setup done.
> Experimentation with a system of similar age suggested another candidate.
> System has a conventional BIOS.  Might some dependancies on the presence
> of UEFI snuck into the NPT code?

I can't think of any such, but as all of this is very nebulous I can't
really rule out anything.




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