linux-kernel - Re: [PATCH 1/8] iommu: Introduce a replace API for device pasid

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Date: Thu, 21 Mar 2024 21:58:08 +0800
From: Yi Liu <yi.l.liu@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Baolu Lu <baolu.lu@...ux.intel.com>, "Tian, Kevin" <kevin.tian@...el.com>,
	"joro@...tes.org" <joro@...tes.org>, "alex.williamson@...hat.com"
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 Zhenzhong" <zhenzhong.duan@...el.com>, "joao.m.martins@...cle.com"
	<joao.m.martins@...cle.com>, "Zeng, Xin" <xin.zeng@...el.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>
Subject: Re: [PATCH 1/8] iommu: Introduce a replace API for device pasid

On 2024/3/21 20:20, Jason Gunthorpe wrote:
> On Thu, Mar 21, 2024 at 07:26:41PM +0800, Yi Liu wrote:
>>> yes, the correct way is to undo what have been done before the fail
>>> device. However, I somehow remember that pasid capability is only
>>> available when the group is singleton. So iterate all devices of the
>>> devices just means one device in fact. If this is true, then the
>>> current code is fine although a bit confusing.
> 
> Platform devicse don't have that limitation.. It is PCI only.

ok.

>>>> And the whole thing is easier to reason about if an input argument
>>>> specifies the current attached domain instead of having the driver
>>>> read it from the xarray.
>>>
>>> yep, will correct it as a fix patch.
>>
>> Hi Jason,
>>
>> It appears there are two solutions here.
>>
>> First, only undo the devices that have set_dev_pasid successfully in
>> the __iommu_set_group_pasid(), so the problematic
>> __iommu_remove_group_pasid() call at line 3378 [1] would go away.
>> This also makes the helper more self-contained. Draft patch in [2]
>>
>> Second, pass in the domain to remove_dev_pasid(). Draft patch in [3]
>>
>> Either of the above two should be able to solve the mistake you mentioned.
>> BTW. They are orthogonal, so it's also possible to apply both of them.
>> Which one is your preference then?
> 
> I would do both because I also think it is not nice that the drivers
> always have to have the boiler plate to read the xarray in their
> remove..

sure. I'll send the two patches as Fix series.

-- 
Regards,
Yi Liu