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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6d8eb619443sm50877846d6.26.2024.12.10.11.13.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Dec 2024 11:13:35 -0800 (PST) Date: Tue, 10 Dec 2024 14:13:29 -0500 From: Gregory Price To: Hongjian Fan Cc: Jonathan Cameron , "qemu-devel@nongnu.org" , "linux-cxl@vger.kernel.org" , "fan.ni@samsung.com" Subject: Re: [PATCH] hw/mem: support zero memory size CXL device Message-ID: References: <20241202230310.1531219-1-hongjian.fan@seagate.com> <20241203172328.00001a00@huawei.com> Precedence: bulk X-Mailing-List: linux-cxl@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: On Tue, Dec 03, 2024 at 09:15:51PM +0000, Hongjian Fan wrote: > Hi Jonathan, > > I'm trying to emulate our memory appliance which is similar to a MH-SLD. The memory device is connected to the host server while the size of the memory could be changed by the out-of-band fabric manager. If there is no memory assigned to the host, the CXL device will be booted as zero memory size. This should not be how this is done. The ACPI tables should report the maximum possible size, and the DCD infrastructure should enable physical regions that have been added to the host. Changing ACPI tables to report 0 memory size will basically result in the host memory map not reserving physical memory regions for that device. See this emulation example of an MHSLD - which can be used for DCD. https://lore.kernel.org/linux-cxl/20241018161252.8896-1-gourry@gourry.net/ > Recently we got some interest on trying our fabric manager software without having the real hardware. Supporting zero memory size in QEMU will be needed in this scenario. > Some detail about our memory appliance could be found from our OCP presentation: https://drive.google.com/file/d/1i8kBsBfRGjNqnTQqJ9upC-Xm9o56Y2Y5/view?usp=drive_link > > Thanks, > Hongjian Fan > > > Seagate Internal