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Tue, 13 Aug 2024 11:02:40 -0700 (PDT) Received: from ziepe.ca ([128.77.69.90]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7a4c7dedffcsm361365585a.80.2024.08.13.11.02.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Aug 2024 11:02:39 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1sdvqw-008qzt-MW; Tue, 13 Aug 2024 15:02:38 -0300 Date: Tue, 13 Aug 2024 15:02:38 -0300 From: Jason Gunthorpe To: Alex Williamson Cc: Keith Busch , kvm@vger.kernel.org, Keith Busch Subject: Re: [PATCH rfc] vfio-pci: Allow write combining Message-ID: <20240813180238.GP1985367@ziepe.ca> References: <20240801171355.GA4830@ziepe.ca> <20240801113344.1d5b5bfe.alex.williamson@redhat.com> <20240801175339.GB4830@ziepe.ca> <20240801121657.20f0fdb4.alex.williamson@redhat.com> <20240802115308.GA676757@ziepe.ca> <20240802110506.23815394.alex.williamson@redhat.com> <20240806165312.GI676757@ziepe.ca> <20240806124302.21e46cee.alex.williamson@redhat.com> <20240807141910.GG8473@ziepe.ca> <20240807114643.25f78652.alex.williamson@redhat.com> 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-Disposition: inline In-Reply-To: <20240807114643.25f78652.alex.williamson@redhat.com> On Wed, Aug 07, 2024 at 11:46:43AM -0600, Alex Williamson wrote: > Please tell me how this is ultimately different from invoking a > DEVICE_FEATURE call to request that a new device specific region be > created with the desired mappings. I think this is more complex for userspace and the drivers to implement than just asking for a new pgoff directly.. A new pgoff we can manage pretty much generically with some new core code, some driver helpers, and adjusting the drivers to use the new helpers. I did exactly this a few years back to rdma and it was not hard. Dynamic region indexes, and indexes that alias other regions, seems more tricky to me. I'm not sure how this would look. It gets to the same place, I agree. Jason