From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Date: Tue, 17 Mar 2020 12:24:45 +0000
Subject: Re: [PATCH 3/4] mm: simplify device private page handling in hmm_range_fault
Message-Id: <20200317122445.GA11662@lst.de>
List-Id: <kvm-ppc.vger.kernel.org>
References: <20200316193216.920734-1-hch@lst.de> <20200316193216.920734-4-hch@lst.de> <7256f88d-809e-4aba-3c46-a223bd8cc521@nvidia.com> <20200317121536.GQ20941@ziepe.ca>
In-Reply-To: <20200317121536.GQ20941@ziepe.ca>
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To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Ralph Campbell <rcampbell@nvidia.com>, Christoph Hellwig <hch@lst.de>, Dan Williams <dan.j.williams@intel.com>, Bharata B Rao <bharata@linux.ibm.com>, Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>, Ben Skeggs <bskeggs@redhat.com>, Jerome Glisse <jglisse@redhat.com>, 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 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.