Re: [PATCH v6 07/10] iommufd: Add a nested HW pagetable object

Yi Liu
2023-10-25T04:07:18Z

On 2023/10/25 02:19, Nicolin Chen wrote:
> On Tue, Oct 24, 2023 at 03:00:49PM -0300, Jason Gunthorpe wrote:
>> On Tue, Oct 24, 2023 at 10:50:58AM -0700, Nicolin Chen wrote:
>>
>>>> The point is for the user_data to always be available, the driver
>>>> needs to check it if it is passed.
>>>>
>>>> This should all be plumbed to allow drivers to also customize their
>>>> paging domains too.
>>>
>>> We don't have a use case of customizing the paging domains.
>>> And our selftest isn't covering this path. Nor the case is
>>> supported by the uAPI:
>>
>> But this is the design, it is why everything is setup like this - we
>> didn't create a new op to allocate nesting domains, we made a flexible
>> user allocator.
>>
>>> 458- * A kernel-managed HWPT will be created with the mappings from the given
>>> 459- * IOAS via the @pt_id. The @data_type for this allocation must be set to
>>> 460: * IOMMU_HWPT_DATA_NONE. The HWPT can be allocated as a parent HWPT for a
>>> 461- * nesting configuration by passing IOMMU_HWPT_ALLOC_NEST_PARENT via @flags.
>>> 462- *
>>
>> Yes, that is the reality today. If someone comes to use the more
>> complete interface they need to fix that comment..
>
> Ack.
>
>>> Also, if we do passing in the data, we'd need to...
>>
>>> 280-static struct iommu_domain *
>>> 281-mock_domain_alloc_user(struct device *dev, u32 flags,
>>> 282- struct iommu_domain *parent,
>>> 283: const struct iommu_user_data *user_data)
>>> 284-{
>>> 285- struct mock_iommu_domain *mock_parent;
>>> 286- struct iommu_hwpt_selftest user_cfg;
>>> 287- int rc;
>>> 288-
>>> 289: if (!user_data) { /* must be mock_domain */
>>>
>>> ...change this to if (!parent)...
>>
>> Yes, this logic is not ideal. The parent is the request for nesting,
>> not user_data. user_data is the generic creation parameters, which are
>> not supported outside nesting
>>
>> Like this:
>>
>> --- a/drivers/iommu/iommufd/selftest.c
>> +++ b/drivers/iommu/iommufd/selftest.c
>> @@ -286,14 +286,12 @@ mock_domain_alloc_user(struct device *dev, u32 flags,
>> int rc;
>>
>> /* must be mock_domain */
>> - if (!user_data) {
>> + if (!parent) {
>> struct mock_dev *mdev = container_of(dev, struct mock_dev, dev);
>> bool has_dirty_flag = flags & IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
>> bool no_dirty_ops = mdev->flags & MOCK_FLAGS_DEVICE_NO_DIRTY;
>>
>> - if (parent)
>> - return ERR_PTR(-EINVAL);
>> - if (has_dirty_flag && no_dirty_ops)
>> + if (user_data || (has_dirty_flag && no_dirty_ops))
>> return ERR_PTR(-EOPNOTSUPP);
>> return __mock_domain_alloc_paging(IOMMU_DOMAIN_UNMANAGED,
>> has_dirty_flag);
>
> Yea.. Then the vt-d driver needs a similar change too (@Yi) as I
> found it almost doing the same:
> https://lore.kernel.org/linux-iommu/20231024151412.50046-8-yi.l.liu@intel.com/
>
yes. mock driver is kind of sample code, so the intel iommu driver is doing
almost the same thing. will follow up with the branch Jason shared.

--
Regards,
Yi Liu