Re: [PATCH v2 1/2] iommu/virtio: Make use of ops->iotlb_sync_map

[Baolu Lu <baolu.lu@linux.intel.com>]

On 9/23/23 7:33 AM, Jason Gunthorpe wrote:
> On Fri, Sep 22, 2023 at 07:07:40PM +0100, Robin Murphy wrote:
> 
>> virtio isn't setting ops->pgsize_bitmap for the sake of direct mappings
>> either; it sets it once it's discovered any instance, since apparently it's
>> assuming that all instances must support identical page sizes, and thus once
>> it's seen one it can work "normally" per the core code's assumptions. It's
>> also I think the only driver which has a "finalise" bodge but*can*  still
>> properly support map-before-attach, by virtue of having to replay mappings
>> to every new endpoint anyway.
> Well it can't quite do that since it doesn't know the geometry - it
> all is sort of guessing and hoping it doesn't explode on replay. If it
> knows the geometry it wouldn't need finalize...

The ultimate solution to this problem seems to be to add device pointer
to the parameter of ops->domain_alloc. So once the domain is allocated,
it is fully initialized. Attaching this domain to a device that is not
compatible will return -EINVAL, then the caller has to allocate a new
domain for this device.

I feel that this is not an AMD specific problem, other iommu drivers
will also encounter the similar problem sooner or later.

Best regards,
baolu