linux-kernel - Re: [RFC PATCH] iommufd: Destroy vdevice on device unbind

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Message-ID: <20250613124202.GD1130869@ziepe.ca>
Date: Fri, 13 Jun 2025 09:42:02 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@...nel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>
Subject: Re: [RFC PATCH] iommufd: Destroy vdevice on device unbind

On Fri, Jun 13, 2025 at 07:31:48AM +0000, Tian, Kevin wrote:
> yeah that seems to be the option if the said life-cycle dependency
> cannot be removed...
> 
> conceptually it's still a bit unclean as the user needs to know that
> the vdevice object is special after idevice is unbound i.e. it can only
> be destroyed instead of supporting any other kind of operations.

I would say userspace is somewhat malfunctioning if it destroys vfio
before the vdevice. So the main aim here should be to contain the
resulting mess, but still expect userspace to destroy the vdevice
without a failure.

> hmm if the user needs to build certain knowledge anyway can we 
> go one step further to state that the vdevice will be destroyed
> automatically once its idevice is unbound so the user shouldn't
> attempt to explicitly destroy it again after unbind?

I would assume a malfunctioning userspace is probably going to destroy
the vdevice explicitly. If it had proper knowledge it wouldn't have
done this in the first place :)

Jason