linux-kernel - Re: [PATCH v6 04/10] iommu: Extend domain attach group with handle support

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Date: Thu, 13 Jun 2024 12:47:55 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, Kevin Tian <kevin.tian@...el.com>,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Nicolin Chen <nicolinc@...dia.com>, Yi Liu <yi.l.liu@...el.com>,
 Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 Joel Granados <j.granados@...sung.com>, iommu@...ts.linux.dev,
 virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 04/10] iommu: Extend domain attach group with handle
 support

On 6/12/24 9:41 PM, Jason Gunthorpe wrote:
> On Mon, May 27, 2024 at 12:05:11PM +0800, Lu Baolu wrote:
>> Unlike the SVA case where each PASID of a device has an SVA domain
>> attached to it, the I/O page faults are handled by the fault handler
>> of the SVA domain. The I/O page faults for a user page table might
>> be handled by the domain attached to RID or the domain attached to
>> the PASID, depending on whether the PASID table is managed by user
>> space or kernel. As a result, there is a need for the domain attach
>> group interfaces to have attach handle support. The attach handle
>> will be forwarded to the fault handler of the user domain.
>>
>> Add some variants of the domain attaching group interfaces so that they
>> could support the attach handle and export them for use in IOMMUFD.
>>
>> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/iommu-priv.h |  8 +++
>>   drivers/iommu/iommu.c      | 99 ++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 107 insertions(+)
> I don't have an objection to it like this, but I wonder if we could be
> smaller to teach iommu_attach_device_pasid to use IOMMU_NO_PASID to
> attach the handle to the rid?
> 
> It would have an if there to call the  __iommu_attach_group() instead
> of the pasid attach ?

This is a good idea. I guess that in the future, we will have
iommu_attach_device_pasid(IOMMU_NO_PASID) to replace
iommu_attach_group(). The group->domain and domain_ops::attach_dev will
also be removed.

I'd suggest making such refactoring in a separate series with wider
discussions. For now, let's make this special interface for iommufd.

Best regards,
baolu