Re: [PATCH for-4.15 3/4] [RFC] xen/iommu: x86: Clear the root page-table before freeing the page-tables

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.12.2020 15:56, Julien Grall wrote:
> On 23/12/2020 14:12, Jan Beulich wrote:
>> On 22.12.2020 16:43, Julien Grall wrote:
>>> This is an RFC because it would break AMD IOMMU driver. One option would
>>> be to move the call to the teardown callback earlier on. Any opinions?
>>
>> We already have
>>
>> static void amd_iommu_domain_destroy(struct domain *d)
>> {
>>      dom_iommu(d)->arch.amd.root_table = NULL;
>> }
>>
>> and this function is AMD's teardown handler. Hence I suppose
>> doing the same for VT-d would be quite reasonable. And really
>> VT-d's iommu_domain_teardown() also already has
>>
>>      hd->arch.vtd.pgd_maddr = 0;
> 
> Let me have a look if that works.
> 
>>
>> I guess what's missing is prevention of the root table
>> getting re-setup. 
> 
> This is taken care in the follow-up patch by forbidding page-table 
> allocation. I can mention it in the commit message.

My expectation is that with that subsequent change the change here
(or any variant of it) would become unnecessary.

Jan