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Mon, 27 Oct 2025 22:17:12 -0400 (EDT) Date: Mon, 27 Oct 2025 20:17:11 -0600 From: Alex Williamson To: Mukesh R Cc: alex.williamson@redhat.com, joe@perches.com, kvm@vger.kernel.org, "linux-kernel@vger.kernel.org" , "linux-hyperv@vger.kernel.org" , "wei.liu@kernel.org" Subject: Re: [RFC] Making vma_to_pfn() public (due to vm_pgoff change) Message-ID: <20251027201711.65e82a4f@shazbot.org> In-Reply-To: References: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 27 Oct 2025 14:21:56 -0700 Mukesh R wrote: > Hi Alex, > > This regards vfio passthru support on hyperv running linux as dom0 aka > root. At a high level, cloud hypervisor uses vfio for set up as usual, > then maps the mmio ranges via the hyperv linux driver ioctls. > > Over a year ago, when working on this I had used vm_pgoff to get the pfn > for the mmio, that was 5.15 and early 6.x kernels. Now that I am porting > to 6.18 for upstreaming, I noticed: > > commit aac6db75a9fc > Author: Alex Williamson > vfio/pci: Use unmap_mapping_range() > > changed the behavior and vm_pgoff is no longer holding the pfn. In light > of that, I wondered if the following minor change, making vma_to_pfn() > public (after renaming it), would be acceptable to you. How do you know the device is using vfio_pci_core_mmap() with these semantics for vm_pgoff versus something like nvgrace_gpu_mmap() that uses vm_pgoff more like you're expecting? vma_to_pfn() is specific to the vfio-pci-core semantics, it's not portable to expose for other use cases. Thanks, Alex