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[159.2.73.22]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-89ecf865ccesm66356736d6.39.2026.03.30.08.56.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Mar 2026 08:56:52 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1w7Eyx-00000003cgN-4AHM; Mon, 30 Mar 2026 12:56:52 -0300 Date: Mon, 30 Mar 2026 12:56:51 -0300 From: Jason Gunthorpe To: Alex Williamson Cc: Niklas Schnelle , Farhan Ali , Julian Ruess , wintera@linux.ibm.com, ts@linux.ibm.com, oberpar@linux.ibm.com, gbayer@linux.ibm.com, Yishai Hadas , Shameer Kolothum , Kevin Tian , mjrosato@linux.ibm.com, raspl@linux.ibm.com, hca@linux.ibm.com, agordeev@linux.ibm.com, gor@linux.ibm.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-pci@vger.kernel.org Subject: Re: [PATCH v8 2/3] vfio/ism: Implement vfio_pci driver for ISM devices Message-ID: <20260330155651.GD246076@ziepe.ca> References: <20260325-vfio_pci_ism-v8-0-ddc504cde914@linux.ibm.com> <20260325-vfio_pci_ism-v8-2-ddc504cde914@linux.ibm.com> <4096cb9d402b1aabc9667d450221cb0922e78d90.camel@linux.ibm.com> <3d6457b9-715a-4cbb-9c69-d8a7e7473c89@linux.ibm.com> <64e3158a441c79c55febead9aac956c31f034fb9.camel@linux.ibm.com> <20260330093646.03b0455f@shazbot.org> 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: <20260330093646.03b0455f@shazbot.org> On Mon, Mar 30, 2026 at 09:36:46AM -0600, Alex Williamson wrote: > There's risk involved with changing the default shift. The fear is > there's userspace drivers that hard code the shift. DPDK was even such > a user at one point, iirc. Maybe it's ok to break such users, maybe > there are actually no such users left and it's all FUD at this point. > Either way, I have a hard time justifying that risk for a single, > obscure S390 device. If we go ahead with that DMABUF series could obscure cases like this be told to just get a DMABUF FD and then mmap it? Avoid this whole issue? Jason