linux-kernel - Re: [RFC PATCH 13/15] iommufd: Persist iommu domains for live update

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Message-ID: <CA+CK2bBvY7A-PBozXC7DQwza6OqETe_x3XasuUx9VJBKWkZR-A@mail.gmail.com>
Date: Thu, 2 Oct 2025 10:59:05 -0400
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Samiullah Khawaja <skhawaja@...gle.com>, David Woodhouse <dwmw2@...radead.org>, 
	Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, 
	Will Deacon <will@...nel.org>, iommu@...ts.linux.dev, YiFei Zhu <zhuyifei@...gle.com>, 
	Robin Murphy <robin.murphy@....com>, Pratyush Yadav <pratyush@...nel.org>, 
	Kevin Tian <kevin.tian@...el.com>, linux-kernel@...r.kernel.org, 
	Saeed Mahameed <saeedm@...dia.com>, Adithya Jayachandran <ajayachandra@...dia.com>, 
	Parav Pandit <parav@...dia.com>, Leon Romanovsky <leonro@...dia.com>, William Tu <witu@...dia.com>, 
	Vipin Sharma <vipinsh@...gle.com>, dmatlack@...gle.com, Chris Li <chrisl@...nel.org>, 
	praan@...gle.com
Subject: Re: [RFC PATCH 13/15] iommufd: Persist iommu domains for live update

On Thu, Oct 2, 2025 at 9:41 AM Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> On Wed, Oct 01, 2025 at 06:00:58PM -0700, Samiullah Khawaja wrote:
> > > No, finish should never do anything on the restore path, IMHO. User
> > > should directly attach the newly created HWPT when it is ready.
> >
> > Makes sense. But if the user never replaces the restored iommu_domain
> > with a new HWPT, we will have to discard the old (restored) domain on
> > finish since it doesn't have any associated HWPT. I see you already
> > hinted at this below. This needs to be handled carefully considering
> > the vfio cdev FD state also. Discussed further below.
>
> I think the simplest thing is the domain exists forever until
> userspace attaches an iommufd, takes ownership of it and frees it.
> Nothing to do with finish.
>
> While the domain is attached iommu_device_use_default_domain() will
> fail.

Ah you answered my question from my previous email, let me talk to Sami.