From mboxrd@z Thu Jan 1 00:00:00 1970 From: Logan Gunthorpe Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma Date: Wed, 30 Jan 2019 14:01:35 -0700 Message-ID: <35bad6d5-c06b-f2a3-08e6-2ed0197c8691@deltatee.com> References: <20190129205749.GN3176@redhat.com> <2b704e96-9c7c-3024-b87f-364b9ba22208@deltatee.com> <20190129215028.GQ3176@redhat.com> <20190129234752.GR3176@redhat.com> <655a335c-ab91-d1fc-1ed3-b5f0d37c6226@deltatee.com> <20190130041841.GB30598@mellanox.com> <20190130080006.GB29665@lst.de> <20190130190651.GC17080@mellanox.com> <840256f8-0714-5d7d-e5f5-c96aec5c2c05@deltatee.com> <20190130195900.GG17080@mellanox.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190130195900.GG17080-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Jason Gunthorpe Cc: Joerg Roedel , "Rafael J . Wysocki" , Greg Kroah-Hartman , Felix Kuehling , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org" , Christian Koenig , "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" , Jerome Glisse , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Bjorn Helgaas , Robin Murphy , Christoph Hellwig List-Id: iommu@lists.linux-foundation.org On 2019-01-30 12:59 p.m., Jason Gunthorpe wrote: > On Wed, Jan 30, 2019 at 12:45:46PM -0700, Logan Gunthorpe wrote: >> >> >> On 2019-01-30 12:06 p.m., Jason Gunthorpe wrote: >>>> Way less problems than not having struct page for doing anything >>>> non-trivial. If you map the BAR to userspace with remap_pfn_range >>>> and friends the mapping is indeed very simple. But any operation >>>> that expects a page structure, which is at least everything using >>>> get_user_pages won't work. >>> >>> GUP doesn't work anyhow today, and won't work with BAR struct pages in >>> the forseeable future (Logan has sent attempts on this before). >> >> I don't recall ever attempting that... But patching GUP for special >> pages or VMAS; or working around by not calling it in some cases seems >> like the thing that's going to need to be done one way or another. > > Remember, the long discussion we had about how to get the IOMEM > annotation into SGL? That is a necessary pre-condition to doing > anything with GUP in DMA using drivers as GUP -> SGL -> DMA map is > pretty much the standard flow. Yes, but that was unrelated to GUP even if that might have been the eventual direction. And I feel the GUP->SGL->DMA flow should still be what we are aiming for. Even if we need a special GUP for special pages, and a special DMA map; and the SGL still has to be homogenous.... > So, I see Jerome solving the GUP problem by replacing GUP entirely > using an API that is more suited to what these sorts of drivers > actually need. Yes, this is what I'm expecting and what I want. Not bypassing the whole thing by doing special things with VMAs. Logan