From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Date: Tue, 17 Mar 2020 12:28:13 +0000 Subject: Re: [PATCH 3/4] mm: simplify device private page handling in hmm_range_fault Message-Id: <20200317122813.GA11866@lst.de> List-Id: References: <20200316193216.920734-1-hch@lst.de> <20200316193216.920734-4-hch@lst.de> <7256f88d-809e-4aba-3c46-a223bd8cc521@nvidia.com> <20200317121536.GQ20941@ziepe.ca> <20200317122445.GA11662@lst.de> In-Reply-To: <20200317122445.GA11662@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Jason Gunthorpe Cc: Ralph Campbell , Christoph Hellwig , Dan Williams , Bharata B Rao , Christian =?iso-8859-1?Q?K=F6nig?= , Ben Skeggs , Jerome Glisse , kvm-ppc@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, linux-mm@kvack.org On Tue, Mar 17, 2020 at 01:24:45PM +0100, Christoph Hellwig wrote: > On Tue, Mar 17, 2020 at 09:15:36AM -0300, Jason Gunthorpe wrote: > > > Getting rid of HMM_PFN_DEVICE_PRIVATE seems reasonable to me since a driver can > > > look at the struct page but what if a driver needs to fault in a page from > > > another device's private memory? Should it call handle_mm_fault()? > > > > Isn't that what this series basically does? > > > > The dev_private_owner is set to the type of pgmap the device knows how > > to handle, and everything else is automatically faulted for the > > device. > > > > If the device does not know how to handle device_private then it sets > > dev_private_owner to NULL and it never gets device_private pfns. > > > > Since the device_private pfn cannot be dma mapped, drivers must have > > explicit support for them. > > No, with this series (and all actual callers before this series) > we never fault in device private pages. IFF we want to fault it in we'd need something like this. But I'd really prefer to see test cases for that first. diff --git a/mm/hmm.c b/mm/hmm.c index b75b3750e03d..2884a3d11a1f 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -276,7 +276,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, if (!fault && !write_fault) return 0; - if (!non_swap_entry(entry)) + if (!non_swap_entry(entry) || is_device_private_entry(entry)) goto fault; if (is_migration_entry(entry)) {