linux-kernel - Re: [PATCH v8 10/11] vfio/pci: Add dma-buf export support for MMIO regions

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Message-ID: <20251119194120.GR17968@ziepe.ca>
Date: Wed, 19 Nov 2025 15:41:20 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Leon Romanovsky <leon@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>, Jens Axboe <axboe@...nel.dk>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Kees Cook <kees@...nel.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Ankit Agrawal <ankita@...dia.com>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <skolothumtho@...dia.com>,
	Alex Williamson <alex@...zbot.org>,
	Krishnakant Jaju <kjaju@...dia.com>, Matt Ochs <mochs@...dia.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
	"Kasireddy, Vivek" <vivek.kasireddy@...el.com>
Subject: Re: [PATCH v8 10/11] vfio/pci: Add dma-buf export support for MMIO
 regions

On Tue, Nov 18, 2025 at 11:56:14PM +0000, Tian, Kevin wrote:
> > > > +	down_write(&vdev->memory_lock);
> > > > +	list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm)
> > > > {
> > > > +		if (!get_file_active(&priv->dmabuf->file))
> > > > +			continue;
> > > > +
> > > > +		dma_resv_lock(priv->dmabuf->resv, NULL);
> > > > +		list_del_init(&priv->dmabufs_elm);
> > > > +		priv->vdev = NULL;
> > > > +		priv->revoked = true;
> > > > +		dma_buf_move_notify(priv->dmabuf);
> > > > +		dma_resv_unlock(priv->dmabuf->resv);
> > > > +		vfio_device_put_registration(&vdev->vdev);
> > > > +		fput(priv->dmabuf->file);
> > >
> > > dma_buf_put(priv->dmabuf), consistent with other places.
> > 
> > Someone else said this, I don't agree, the above got the get via
> > 
> > get_file_active() instead of a dma_buf version..
> > 
> > So we should pair with get_file_active() vs fput().
> > 
> > Christian rejected the idea of adding a dmabuf wrapper for
> > get_file_active(), oh well.
> 
> Okay then vfio_pci_dma_buf_move() should be changed. It uses
> get_file_active() to pair dma_buf_put().

Makes sense, Leon can you fix it?

Thanks,
Jason