From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH 04/15] mm: remove the pgmap field from struct hmm_vma_walk Date: Fri, 16 Aug 2019 14:28:46 -0300 Message-ID: <20190816172846.GJ5398@ziepe.ca> References: <20190815194339.GC9253@redhat.com> <20190815203306.GB25517@redhat.com> <20190815204128.GI22970@mellanox.com> <20190816004053.GB9929@mellanox.com> <20190816122414.GC5412@mellanox.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Dan Williams Cc: Jerome Glisse , Christoph Hellwig , Ben Skeggs , Felix Kuehling , Ralph Campbell , "linux-mm@kvack.org" , "nouveau@lists.freedesktop.org" , "dri-devel@lists.freedesktop.org" , "amd-gfx@lists.freedesktop.org" , "linux-kernel@vger.kernel.org" List-Id: dri-devel@lists.freedesktop.org On Fri, Aug 16, 2019 at 10:21:41AM -0700, Dan Williams wrote: > > We can do a get_dev_pagemap inside the page_walk and touch the pgmap, > > or we can do the 'device mutex && retry' pattern and touch the pgmap > > in the driver, under that lock. > > > > However in all cases the current get_dev_pagemap()'s in the page walk > > are not necessary, and we can delete them. > > Yes, as long as 'struct page' instances resulting from that lookup are > not passed outside of that lock. Indeed. Also, I was reflecting over lunch that the hmm_range_fault should only return DEVICE_PRIVATE pages for the caller's device (see other thread with HCH), and in this case, the caller should also be responsible to ensure that the driver is not calling hmm_range_fault at the same time it is deleting it's own DEVICE_PRIVATE mapping - ie by fencing its page fault handler. This does not apply to PCI_P2PDMA, but, lets see how that looks when we get there. So the whole thing seems pretty safe. Jason