linux-kernel - Re: [PATCH v5 9/9] vfio/pci: Add dma-buf export support for MMIO regions

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Message-ID: <20251017155850.GN3901471@nvidia.com>
Date: Fri, 17 Oct 2025 12:58:50 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Leon Romanovsky <leon@...nel.org>
Cc: Alex Williamson <alex.williamson@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Christian König <christian.koenig@....com>,
	dri-devel@...ts.freedesktop.org, iommu@...ts.linux.dev,
	Jens Axboe <axboe@...nel.dk>, Joerg Roedel <joro@...tes.org>,
	kvm@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org, linux-mm@...ck.org,
	linux-pci@...r.kernel.org, Logan Gunthorpe <logang@...tatee.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH v5 9/9] vfio/pci: Add dma-buf export support for MMIO
 regions

On Fri, Oct 17, 2025 at 08:40:07AM +0300, Leon Romanovsky wrote:
> > > +static void vfio_pci_dma_buf_detach(struct dma_buf *dmabuf,
> > > +				    struct dma_buf_attachment *attachment)
> > > +{
> > > +	kfree(attachment->priv);
> > > +}
> > 
> > If the caller fails to call map then it leaks the iova.
> 
> I'm relying on dmabuf code and documentation:
> 
>    926 /**
>    927  * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list
> ...   
>    932  *
>    933  * Returns struct dma_buf_attachment pointer for this attachment. Attachments
>    934  * must be cleaned up by calling dma_buf_detach().
> 
> Successful call to vfio_pci_dma_buf_attach() MUST be accompanied by call
> to vfio_pci_dma_buf_detach(), so as far as dmabuf implementation follows
> it, there is no leak.

It leaks the ivoa because there is no dma_iova_destroy() unless you
call unmap. detach is not unmap and unmap is not mandatory to call.

Jason