linux-kernel - Re: [PATCH v3 1/5] iommufd: Add iommufd_object_tombstone

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Message-ID: <aGzauAtJrUXS1Q/a@yilunxu-OptiPlex-7050>
Date: Tue, 8 Jul 2025 16:45:44 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, jgg@...pe.ca, kevin.tian@...el.com, will@...nel.org,
	aneesh.kumar@...nel.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, joro@...tes.org, robin.murphy@....com,
	shuah@...nel.org, aik@....com, dan.j.williams@...el.com,
	baolu.lu@...ux.intel.com, yilun.xu@...el.com
Subject: Re: [PATCH v3 1/5] iommufd: Add iommufd_object_tombstone_user()
 helper

On Mon, Jun 30, 2025 at 12:50:57PM -0700, Nicolin Chen wrote:
> On Fri, Jun 27, 2025 at 11:38:05AM +0800, Xu Yilun wrote:
> > Add the iommufd_object_tombstone_user() helper, which allows the caller
> > to destroy an iommufd object created by userspace.
> 
> Should we describe it "partially destroy"?

I don't prefer "partially destroy", it gives the impression the object
is still in memory, in fact with the helper it is totally destroyed and
freed. Only the ID is reserved, but the ID actually has nothing to do
with the object anymore.

> 
> > This is useful on some destroy paths when the kernel caller finds the
> > object should have been removed by userspace but is still alive. With
> > this helper, the caller destroys the object but leave the object ID
> > reserved (so called tombstone). The tombstone prevents repurposing the
> > object ID without awareness of the original user.
> > 
> > Since this happens for abnomal userspace behavior, for simplicity, the
> 
> s/abnomal/abnormal

Applied, thanks for catching.

> 
> Nicolin