linux-kernel - Re: [RFC PATCH 2/2] RDMA/efa: Add support for dmabuf memory regions

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Message-ID: <20211011232839.GF2688930@ziepe.ca>
Date:   Mon, 11 Oct 2021 20:28:39 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Gal Pressman <galpress@...zon.com>
Cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Doug Ledford <dledford@...hat.com>,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        Oded Gabbay <ogabbay@...ana.ai>,
        Tomer Tayar <ttayar@...ana.ai>,
        Yossi Leybovich <sleybo@...zon.com>,
        Alexander Matushevsky <matua@...zon.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Jianxin Xiong <jianxin.xiong@...el.com>,
        Firas Jahjah <firasj@...zon.com>
Subject: Re: [RFC PATCH 2/2] RDMA/efa: Add support for dmabuf memory regions

On Sun, Oct 10, 2021 at 09:55:49AM +0300, Gal Pressman wrote:
> On 07/10/2021 14:40, Jason Gunthorpe wrote:
> > On Thu, Oct 07, 2021 at 01:43:00PM +0300, Gal Pressman wrote:
> > 
> >> @@ -1491,26 +1493,29 @@ static int efa_create_pbl(struct efa_dev *dev,
> >>  	return 0;
> >>  }
> >>  
> >> -struct ib_mr *efa_reg_mr(struct ib_pd *ibpd, u64 start, u64 length,
> >> -			 u64 virt_addr, int access_flags,
> >> -			 struct ib_udata *udata)
> >> +static void efa_dmabuf_invalidate_cb(struct dma_buf_attachment *attach)
> >> +{
> >> +	WARN_ON_ONCE(1,
> >> +		     "Invalidate callback should not be called when memory is pinned\n");
> >> +}
> >> +
> >> +static struct dma_buf_attach_ops efa_dmabuf_attach_ops = {
> >> +	.allow_peer2peer = true,
> >> +	.move_notify = efa_dmabuf_invalidate_cb,
> >> +};
> > 
> > Shouldn't move_notify really just be left as NULL? I mean fixing
> > whatever is preventing that?
> 
> That's what I had in the previous RFC and I think Christian didn't really like it.

Well, having drivers define a dummy function that only fails looks
a lot worse to me. If not null then it should be a general
'dmabuf_unsupported_move_notify' shared function

> >> +	err = ib_umem_dmabuf_map_pages(umem_dmabuf);
> >> +	if (err) {
> >> +		ibdev_dbg(&dev->ibdev, "Failed to map dmabuf pages\n");
> >> +		goto err_unpin;
> >> +	}
> >> +	dma_resv_unlock(umem_dmabuf->attach->dmabuf->resv);
> > 
> > If it is really this simple the core code should have this logic,
> > 'ib_umem_dmabuf_get_pinned()' or something
> 
> Should get_pinned do just get + dma_buf_pin, or should it do
> ib_umem_dmabuf_map_pages as well?

Yes the map_pages too, a umem is supposed to be dma mapped after
creation.

Jason