Re: [PATCH v1 2/8] iommu: Introduce a new iommu_group_replace_domain() API

From: Baolu Lu <baolu.lu@linux.intel.com>
To: Nicolin Chen <nicolinc@nvidia.com>
Cc: baolu.lu@linux.intel.com, jgg@nvidia.com, kevin.tian@intel.com,
	joro@8bytes.org, will@kernel.org, robin.murphy@arm.com,
	alex.williamson@redhat.com, shuah@kernel.org, yi.l.liu@intel.com,
	linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
	kvm@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v1 2/8] iommu: Introduce a new iommu_group_replace_domain() API
Date: Fri, 3 Feb 2023 10:35:04 +0800	[thread overview]
Message-ID: <afe65351-8481-63ef-749f-54b151431af3@linux.intel.com> (raw)
In-Reply-To: <Y9xmTRQH7wjb07gl@Asurada-Nvidia>

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