Re: [for-4.15][PATCH v2 1/5] xen/x86: p2m: Don't map the special pages in the IOMMU page-tables

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.02.2021 12:34, Roger Pau Monné wrote:
> On Wed, Feb 10, 2021 at 12:10:09PM +0100, Jan Beulich wrote:
>> On 10.02.2021 09:29, Roger Pau Monné wrote:
>>> I get the feeling this is just papering over an existing issue instead
>>> of actually fixing it: IOMMU page tables need to be properly freed
>>> during early failure.
>>
>> I take a different perspective: IOMMU page tables shouldn't
>> get created (yet) at all in the course of
>> XEN_DOMCTL_createdomain - this op is supposed to produce an
>> empty container for a VM.
> 
> The same would apply for CPU page-tables then, yet they seem to be
> created and populating them (ie: adding the lapic access page) doesn't
> leak such entries, which points at an asymmetry. Either we setup both
> tables and handle freeing them properly, or we set none of them.

Where would CPU page tables get created from at this early stage?
There's no memory assigned to the guest yet, so there's nothing to
map afaics.

Jan