linux-kernel - Re: [RFC PATCH 17/30] iommufd/device: Add TSM Bind/Unbind for TIO support

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Message-ID: <20250603122149.GH376789@nvidia.com>
Date: Tue, 3 Jun 2025 09:21:49 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Xu Yilun <yilun.xu@...ux.intel.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>, kvm@...r.kernel.org,
	sumit.semwal@...aro.org, christian.koenig@....com,
	pbonzini@...hat.com, seanjc@...gle.com, alex.williamson@...hat.com,
	dan.j.williams@...el.com, aik@....com, linux-coco@...ts.linux.dev,
	dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
	linaro-mm-sig@...ts.linaro.org, vivek.kasireddy@...el.com,
	yilun.xu@...el.com, linux-kernel@...r.kernel.org, lukas@...ner.de,
	yan.y.zhao@...el.com, daniel.vetter@...ll.ch, leon@...nel.org,
	baolu.lu@...ux.intel.com, zhenzhong.duan@...el.com,
	tao1.su@...el.com, linux-pci@...r.kernel.org, zhiw@...dia.com,
	simona.vetter@...ll.ch, shameerali.kolothum.thodi@...wei.com,
	iommu@...ts.linux.dev, kevin.tian@...el.com
Subject: Re: [RFC PATCH 17/30] iommufd/device: Add TSM Bind/Unbind for TIO
 support

On Tue, Jun 03, 2025 at 02:20:51PM +0800, Xu Yilun wrote:
> > Wouldn’t it be simpler to skip the reference count increment altogether
> > and just call tsm_unbind in the virtual device’s destroy callback?
> > (iommufd_vdevice_destroy())
> 
> The vdevice refcount is the main concern, there is also an IOMMU_DESTROY
> ioctl. User could just free the vdevice instance if no refcount, while VFIO
> is still in bound state. That seems not the correct free order.

Freeing the vdevice should automatically unbind it..

Jason