Re: [PATCH 1/6] VT-d: properly reserve DID 0 for caching mode IOMMUs

[Jan Beulich <jbeulich@suse.com>]

On 12.11.2021 12:23, Roger Pau Monné wrote:
> On Fri, Nov 12, 2021 at 10:47:59AM +0100, Jan Beulich wrote:
>> Merely setting bit 0 in the bitmap is insufficient, as then Dom0 will
>> still have DID 0 allocated to it, because of the zero-filling of
>> domid_map[]. Set slot 0 to DOMID_INVALID to keep DID 0 from getting
>> used.
> 
> Shouldn't the whole domid_map be initialized to DOMID_INVALID to
> prevent dom0 matching against any unused slot?
> 
> Similarly cleanup_domid_map should set the slot to DOMID_INVALID.

I don't think so, that's the purpose of setting the bit in domid_bitmap.
The problem really was only with setting a bit in that bitmap without
invalidating the corresponding slot.

This said, I can still see value in doing as you suggest, but as a
separate change with a different justification. In fact domid_bitmap is
kind of redundant now anyway; aiui it was the thing that existed first.
Then domid_map[] was simply added, rather than fully replacing the
original bitmap.

Jan