linux-kernel - Re: [PATCH 00/20] iommu: Refactoring domain allocation interface

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Date: Wed, 29 May 2024 20:02:12 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Yi Liu <yi.l.liu@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>, Kevin Tian <kevin.tian@...el.com>
Cc: baolu.lu@...ux.intel.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 00/20] iommu: Refactoring domain allocation interface

On 2024/5/29 17:03, Yi Liu wrote:
> On 2024/5/29 13:32, Lu Baolu wrote:
>> The IOMMU subsystem has undergone some changes, including the removal
>> of iommu_ops from the bus structure. Consequently, the existing domain
>> allocation interface, which relies on a bus type argument, is no longer
>> relevant:
>>
>>      struct iommu_domain *iommu_domain_alloc(struct bus_type *bus)
>>
>> This series is designed to refactor the use of this interface. It
>> proposes two new interfaces to replace iommu_domain_alloc():
>>
>> - iommu_user_domain_alloc(): This interface is intended for allocating
>>    iommu domains managed by userspace for device passthrough scenarios,
>>    such as those used by iommufd, vfio, and vdpa. It clearly indicates
>>    that the domain is for user-managed device DMA.
> 
> user paging domain? It looks to me user domain includes the nested domains
> as well.

Yes, nested domain is a user domain. The iommu driver should implement
iommu_ops->domain_alloc_user for nested domain allocation.

> 
>>    If an IOMMU driver does not implement iommu_ops->domain_alloc_user,
>>    this interface will rollback to the generic paging domain allocation.
>>
>> - iommu_paging_domain_alloc(): This interface is for allocating iommu
>>    domains managed by kernel drivers for kernel DMA purposes. It takes a
>>    device pointer as a parameter, which better reflects the current
>>    design of the IOMMU subsystem.
>>
>> The majority of device drivers currently using iommu_domain_alloc() do
>> so to allocate a domain for a specific device and then attach that
>> domain to the device. These cases can be straightforwardly migrated to
>> the new interfaces.
>>
>> However, there are some drivers with more complex use cases that do
>> not fit neatly into this new scheme. For example:
>>
>> $ git grep "= iommu_domain_alloc"
>> arch/arm/mm/dma-mapping.c:      mapping->domain = 
>> iommu_domain_alloc(bus);
>> drivers/gpu/drm/rockchip/rockchip_drm_drv.c:    private->domain = 
>> iommu_domain_alloc(private->iommu_dev->bus);
>> drivers/gpu/drm/tegra/drm.c:            tegra->domain = 
>> iommu_domain_alloc(&platform_bus_type);
>> drivers/infiniband/hw/usnic/usnic_uiom.c:       pd->domain = domain = 
>> iommu_domain_alloc(dev->bus);
>>
>> This series leave those cases unchanged and keep iommu_domain_alloc()
>> for their usage. But new drivers should not use it anymore.
> 
> does it mean there is still domains allocated via iommu_domain_alloc()
> on VT-d platform?

I think the drivers mentioned above do not run on x86 platforms, or do
they?

Best regards,
baolu