linux-kernel - Re: [PATCH rdma-next 1/2] RDMA/uverbs: Add DMABUF object type and operations

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Message-ID: <20260121083246.GV13201@unreal>
Date: Wed, 21 Jan 2026 10:32:46 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Edward Srouji <edwards@...dia.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org, Yishai Hadas <yishaih@...dia.com>
Subject: Re: [PATCH rdma-next 1/2] RDMA/uverbs: Add DMABUF object type and
 operations

On Tue, Jan 20, 2026 at 02:15:20PM -0400, Jason Gunthorpe wrote:
> On Thu, Jan 08, 2026 at 01:11:14PM +0200, Edward Srouji wrote:
> >  void rdma_user_mmap_entry_remove(struct rdma_user_mmap_entry *entry)
> >  {
> > +	struct ib_uverbs_dmabuf_file *uverbs_dmabuf, *tmp;
> > +
> >  	if (!entry)
> >  		return;
> >  
> > +	mutex_lock(&entry->dmabufs_lock);
> >  	xa_lock(&entry->ucontext->mmap_xa);
> >  	entry->driver_removed = true;
> >  	xa_unlock(&entry->ucontext->mmap_xa);
> > +	list_for_each_entry_safe(uverbs_dmabuf, tmp, &entry->dmabufs, dmabufs_elm) {
> > +		dma_resv_lock(uverbs_dmabuf->dmabuf->resv, NULL);
> > +		list_del(&uverbs_dmabuf->dmabufs_elm);
> > +		uverbs_dmabuf->revoked = true;
> > +		dma_buf_move_notify(uverbs_dmabuf->dmabuf);
> > +		dma_resv_unlock(uverbs_dmabuf->dmabuf->resv);
> 
> This will need the same wait that Christian pointed out for VFIO..

Yes, something like this is missing
https://lore.kernel.org/all/20260120-dmabuf-revoke-v3-6-b7e0b07b8214@nvidia.com/

<...>

> > +struct ib_uverbs_dmabuf_file {
> > +	struct ib_uobject uobj;
> > +	struct dma_buf *dmabuf;
> > +	struct list_head dmabufs_elm;
> > +	struct rdma_user_mmap_entry *mmap_entry;
> > +	struct dma_buf_phys_vec phys_vec;
> 
> Oh, are we going to have weird merge conflicts with this Leon?

No, Alex created a shared branch with the rename already applied for me.  
I had planned to merge it into the RDMA tree before taking this series, and  
then update dma_buf_phys_vec to phys_vec locally.

> 
> > +static int uverbs_dmabuf_attach(struct dma_buf *dmabuf,
> > +				struct dma_buf_attachment *attachment)
> > +{
> > +	struct ib_uverbs_dmabuf_file *priv = dmabuf->priv;
> > +
> > +	if (!attachment->peer2peer)
> > +		return -EOPNOTSUPP;
> > +
> > +	if (priv->revoked)
> > +		return -ENODEV;
> 
> This should only be checked in map

I disagree with word "only", the more accurate word is "too". There is
no need to allow new importer attach if this exporter is marked as
revoked.

> 
> This should also eventually call the new revoke testing function Leon
> is adding

We will add it once my series will be accepted.

Thanks

> 
> Jason