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 16:24, Roger Pau Monné wrote:
> On Wed, Feb 10, 2021 at 02:12:38PM +0100, Jan Beulich wrote:
>> On 10.02.2021 12:54, Roger Pau Monné wrote:
>>> On Wed, Feb 10, 2021 at 11:48:40AM +0000, Julien Grall wrote:
>>>> It feels wrong to me to setup a per-domain mapping when initializing the
>>>> first vCPU.
>>>>
>>>> But, I was under the impression that there is plan to remove
>>>> XEN_DOMCTL_max_vcpus. So it would only buy just a bit of time...
>>>
>>> I was also under that impression. We could setup the lapic access page
>>> at vlapic_init for the BSP (which is part of XEN_DOMCTL_max_vcpus
>>> ATM).
>>>
>>> But then I think there should be some kind of check to prevent
>>> populating either the CPU or the IOMMU page tables at domain creation
>>> hypercall, and so the logic to free CPU table tables on failure could
>>> be removed.
>>
>> I can spot paging_final_teardown() on an error path there, but I
>> don't suppose that's what you mean? I guess I'm not looking in
>> the right place (there are quite a few after all) ...
> 
> Well, I assume some freeing of the EPT page tables must happen on
> error paths, or else we would be leaking them like IOMMU tables are
> leaked currently?

Well, you can't eliminate paging_final_teardown() from that
error path because it frees internal structures. It _also_
sets HAP's / shadow's allocation to zero, so has the side
effect of freeing why may have been CPU page tables.

Jan