linux-kernel - Re: [PATCH v2 02/22] iommufd: Use iommu_user_domain

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Date: Wed, 5 Jun 2024 10:17:07 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Kevin Tian <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 Kalle Valo <kvalo@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
 Mathieu Poirier <mathieu.poirier@...aro.org>,
 Alex Williamson <alex.williamson@...hat.com>, mst@...hat.com,
 Jason Wang <jasowang@...hat.com>, Thierry Reding <thierry.reding@...il.com>,
 Jonathan Hunter <jonathanh@...dia.com>,
 Mikko Perttunen <mperttunen@...dia.com>, iommu@...ts.linux.dev,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/22] iommufd: Use iommu_user_domain_alloc()

On 6/5/24 12:51 AM, Jason Gunthorpe wrote:
> On Tue, Jun 04, 2024 at 09:51:14AM +0800, Lu Baolu wrote:
>> Replace iommu_domain_alloc() with iommu_user_domain_alloc().
>>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/iommufd/hw_pagetable.c | 20 +++++---------------
>>   1 file changed, 5 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
>> index 33d142f8057d..ada05fccb36a 100644
>> --- a/drivers/iommu/iommufd/hw_pagetable.c
>> +++ b/drivers/iommu/iommufd/hw_pagetable.c
>> @@ -127,21 +127,11 @@ iommufd_hwpt_paging_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
>>   	hwpt_paging->ioas = ioas;
>>   	hwpt_paging->nest_parent = flags & IOMMU_HWPT_ALLOC_NEST_PARENT;
>>   
>> -	if (ops->domain_alloc_user) {
>> -		hwpt->domain = ops->domain_alloc_user(idev->dev, flags, NULL,
>> -						      user_data);
>                                                       ^^^^^^^^^^^^
> 
>> -		if (IS_ERR(hwpt->domain)) {
>> -			rc = PTR_ERR(hwpt->domain);
>> -			hwpt->domain = NULL;
>> -			goto out_abort;
>> -		}
>> -		hwpt->domain->owner = ops;
>> -	} else {
>> -		hwpt->domain = iommu_domain_alloc(idev->dev->bus);
>> -		if (!hwpt->domain) {
>> -			rc = -ENOMEM;
>> -			goto out_abort;
>> -		}
>> +	hwpt->domain = iommu_user_domain_alloc(idev->dev, flags);
>> +	if (IS_ERR(hwpt->domain)) {
> 
> Where did the user_data go???

The user_data is not used in allocating a paging user domain, so I
skipped it.

> 
> If you are going to wrapper the op function then all the args need to
> be provided.

Yes. Agreed.

> I'm not sure there is value in having vfio and vdpa call this
> variation since they won't pass a user_data or flags?
> 
> Do you imagine there will ever be a difference between what
> domain_alloc_user(dev, 0, NULL, NULL) returns from
> domain_alloc_paging(dev) ?

No.

> 
> That seems like questionable driver behavior to me.

In my first try, I simply replaced iommu_domain_alloc() with a new
paging domain allocation interface. On second thought, it occurred to me
why not use separate interfaces for different purposes? Even though from
an iommu perspective, they both use paging domains.

The @flags and @user_data are defined in uapi/linux/iommufd.h, which is
specific to iommufd. Wrapping them in a common interface for broader use
seems awkward.

So, perhaps we could return to my original idea? Let's just expose one
interface, iommu_paging_domain_alloc(), and replace iommu_domain_alloc()
with it everywhere?

Best regards,
baolu