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Date: Wed, 3 Jan 2024 10:24:42 +0800
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Subject: Re: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d stage-1
 cache invalidation
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To: Jason Gunthorpe <jgg@nvidia.com>
CC: Nicolin Chen <nicolinc@nvidia.com>, "Tian, Kevin" <kevin.tian@intel.com>,
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References: <20231117131816.24359-1-yi.l.liu@intel.com>
 <20231117131816.24359-2-yi.l.liu@intel.com>
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 <7c398efc-8a2f-479d-bcff-ded8cc1ef3d0@intel.com>
 <20240102233849.GK50406@nvidia.com>
From: Yi Liu <yi.l.liu@intel.com>
In-Reply-To: <20240102233849.GK50406@nvidia.com>
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On 2024/1/3 07:38, Jason Gunthorpe wrote:
> On Fri, Dec 15, 2023 at 12:01:19PM +0800, Yi Liu wrote:
>>> I think I misread Yi's narrative: dev_id is a working approach
>>> for VMM to convert to a vRID, while he is asking for a better
>>> alternative :)
>>
>> In concept, dev_id works, but in reality we have problem to get a dev_id
>> for a given device in intel iommu driver, hence I'm asking for help here. :)
> 
> I think we just need to solve this one way or another.. Even if you
> use a viommu object you still end up having difficult coupling to
> iommufd
> 
> Some:
>    iommufd_get_dev_id(struct iommufd_ctx *ictx, struct device *dev)
> 
> Callable by a driver (using the driver-callable function
> infrastructure we made for dirty tracking) Is really all that is
> needed here.

yep, I noticed IOMMUFD_DRIVER was selected by intel iommu driver when
IOMMUFD is configed. Maybe such an API could be compiled when
IOMMUFD_DRIVER is enabled as well. This does address my concern on making
intel iommu driver depending on iommufd. But still need a way to pass in
the iommufd_ctx pointer to intel iommu driver, and store it. Hence intel
iommu driver could call the above iommufd_get_dev_id(). One possible way is
passing it when attaching device to domain and clear it in detach. However,
this seems not ideal as iommufd_ctx information should be static between
bind_iommufd and unbind. But we don't call into intel iommu driver in the
bind and unbind operations. May need to add new iommu op. Any suggestion
here?

-- 
Regards,
Yi Liu