linux-kernel - Re: [PATCH v2 10/19] iommufd/viommu: Add vdev

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Message-ID: <20241007182816.GD1365916@nvidia.com>
Date: Mon, 7 Oct 2024 15:28:16 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: kevin.tian@...el.com, will@...nel.org, joro@...tes.org,
	suravee.suthikulpanit@....com, robin.murphy@....com,
	dwmw2@...radead.org, baolu.lu@...ux.intel.com, shuah@...nel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, eric.auger@...hat.com,
	jean-philippe@...aro.org, mdf@...nel.org, mshavit@...gle.com,
	shameerali.kolothum.thodi@...wei.com, smostafa@...gle.com,
	yi.l.liu@...el.com
Subject: Re: [PATCH v2 10/19] iommufd/viommu: Add vdev_id helpers for IOMMU
 drivers

On Mon, Oct 07, 2024 at 10:25:01AM -0700, Nicolin Chen wrote:

> This is for vdev/dev v.s. hwpt. We need the lock for viommu's
> vdev xarray.
> 
> Yet, giving a 2nd thought, I feel the lock would be useless if
> a driver tries to refer the returned vdev (with this helper)
> after the vdev object is destroyed..
> 
> We could only note something similar that caller must be aware
> of the life cycle of vdev itself..

Yes, I imagined you'd use the xa_lock for this an it solves both
problems at once.

Jason