linux-kernel - Re: [PATCH v1 2/8] iommu: Introduce a new iommu_group_replace

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Date:   Fri, 3 Feb 2023 10:35:04 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     baolu.lu@...ux.intel.com, jgg@...dia.com, kevin.tian@...el.com,
        joro@...tes.org, will@...nel.org, robin.murphy@....com,
        alex.williamson@...hat.com, shuah@...nel.org, yi.l.liu@...el.com,
        linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v1 2/8] iommu: Introduce a new
 iommu_group_replace_domain() API

On 2023/2/3 9:41, Nicolin Chen wrote:
> On Fri, Feb 03, 2023 at 09:33:44AM +0800, Baolu Lu wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> On 2023/2/3 3:14, Nicolin Chen wrote:
>>> On Thu, Feb 02, 2023 at 06:21:20PM +0800, Baolu Lu wrote:
>>>> External email: Use caution opening links or attachments
>>>>
>>>>
>>>> On 2023/2/2 15:05, Nicolin Chen wrote:
>>>>> +/**
>>>>> + * iommu_group_replace_domain - replace the domain that a group is attached to
>>>>> + * @new_domain: new IOMMU domain to replace with
>>>>> + * @group: IOMMU group that will be attached to the new domain
>>>>> + *
>>>>> + * This API allows the group to switch domains without being forced to go to
>>>>> + * the blocking domain in-between.
>>>>> + *
>>>>> + * If the attached domain is a core domain (e.g. a default_domain), it will act
>>>>> + * just like the iommu_attach_group().
>>>> I am not following above two lines. Why and how could iommufd set a
>>>> core domain to an iommu_group?
>>> Perhaps this isn't the best narrative. What it's supposed to say
>>> is that this function acts as an iommu_attach_group() call if the
>>> device is "detached", yet we have changed the semantics about the
>>> word "detach". So, what should the correct way to write such a
>>> note?
>> How could this interface be used as detaching a domain from a group?
>> Even it could be used, doesn't it act as an iommu_detach_group()?
> No. I didn't say that. It doesn't act as detach(), but attach()
> when a device is already "detached".
> 
> The original statement is saying, "if the attached domain is a
> core domain", i.e. the device is detach()-ed, "it will act just
> like the iommu_attach_group()".

Oh! My bad. I misunderstood it. Sorry for the noise. :-)

Best regards,
baolu