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

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Message-ID: <ZwQ8+ENkxSEaDem4@Asurada-Nvidia>
Date: Mon, 7 Oct 2024 12:56:40 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...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 03:28:16PM -0300, Jason Gunthorpe wrote:
> 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.

Ah! We don't even need a rwsem then..

Thanks!
Nicolin