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

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Message-ID: <Y9xmTRQH7wjb07gl@Asurada-Nvidia>
Date:   Thu, 2 Feb 2023 17:41:33 -0800
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
CC:     <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 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()".

Thanks
Nic