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

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Date:   Wed, 25 Oct 2023 12:05:43 +0800
From:   Yi Liu <yi.l.liu@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     <joro@...tes.org>, <alex.williamson@...hat.com>,
        <kevin.tian@...el.com>, <robin.murphy@....com>,
        <baolu.lu@...ux.intel.com>, <cohuck@...hat.com>,
        <eric.auger@...hat.com>, <kvm@...r.kernel.org>,
        <mjrosato@...ux.ibm.com>, <chao.p.peng@...ux.intel.com>,
        <yi.y.sun@...ux.intel.com>, <peterx@...hat.com>,
        <jasowang@...hat.com>, <shameerali.kolothum.thodi@...wei.com>,
        <lulu@...hat.com>, <suravee.suthikulpanit@....com>,
        <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <zhenzhong.duan@...el.com>,
        <joao.m.martins@...cle.com>
Subject: Re: [PATCH v6 07/10] iommufd: Add a nested HW pagetable object

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