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Fri, 19 Dec 2025 07:13:04 -0800 (PST) Received: from x1.local ([142.188.210.156]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8c0973f28e3sm210526485a.45.2025.12.19.07.13.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Dec 2025 07:13:03 -0800 (PST) Date: Fri, 19 Dec 2025 10:13:02 -0500 From: Peter Xu To: Jason Gunthorpe Cc: kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Nico Pache , Zi Yan , Alex Mastro , David Hildenbrand , Alex Williamson , Zhi Wang , David Laight , Yi Liu , Ankit Agrawal , Kevin Tian , Andrew Morton Subject: Re: [PATCH v2 2/4] mm: Add file_operations.get_mapping_order() Message-ID: References: <20251204151003.171039-3-peterx@redhat.com> <20251216144427.GF6079@nvidia.com> <20251216171944.GG6079@nvidia.com> <20251216185850.GH6079@nvidia.com> <20251219145957.GD254720@nvidia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20251219145957.GD254720@nvidia.com> On Fri, Dec 19, 2025 at 10:59:57AM -0400, Jason Gunthorpe wrote: > On Tue, Dec 16, 2025 at 02:44:29PM -0500, Peter Xu wrote: > > > > Or maybe I misunderstood what you're suggesting to document? If so, please > > > > let me know; some example would be greatly helpful. > > > > > > Just document the 'VA % order = pgoff % order' equation in the kdoc > > > for the new op. > > > > When it's "related to PTEs", it's talking about (2) above, so that's really > > what I want to avoid mentioning. > > You can't avoid it. Drivers must ensure that > > pgoff % order == physical % order > > And that is something only drivers can do by knowing about this > requirement. This is a current limitation that above must be guaranteed, there's not much the driver can do, IMHO. If you could remember, that's the only reason why I used to suggest (while we were discussing this in v1) to make it *pgoff instead of pgoff, so that drivers can change *pgoff to make it relevant to HPA. I didn't take that approach as I want to make this simple until it's justified to be required. It holds true for vfio-pci, I hope it holds true forever. If not, this API will stop working, afaict. -- Peter Xu