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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6ce009e4470sm29298036d6.125.2024.10.22.07.11.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Oct 2024 07:11:56 -0700 (PDT) Date: Tue, 22 Oct 2024 10:11:58 -0400 From: Gregory Price To: Jonathan Cameron Cc: John Groves , David Hildenbrand , linux-mm , linux-cxl , Davidlohr Bueso , Ira Weiny , virtualization , Oscar Salvador , qemu-devel , Dave Jiang , Dan Williams , Linuxarm , "Wangkefeng (OS Kernel Lab)" , John Groves , Fan Ni , Navneet Singh , =?utf-8?B?4oCcTWljaGFlbCBTLiBUc2lya2lu4oCd?= , Igor Mammedov , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Subject: Re: [RFC] Virtualizing tagged disaggregated memory capacity (app specific, multi host shared) Message-ID: References: <20240815172223.00001ca7@Huawei.com> <20240819164024.00005a0a@Huawei.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev 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, Sep 17, 2024 at 07:37:21PM +0000, Jonathan Cameron wrote: > > * Said mechanism should not be explicitly CXL-specific. > > Somewhat agreed, but I don't want to invent a new spec just to avoid explicit > ties to CXL. I'm not against using CXL to present HBM / ACPI Specific Purpose > memory for example to a VM. It will trivially work if that is what a user > wants to do and also illustrates that this stuff doesn't necessarily just > apply to capacity on a memory pool - it might just be 'weird' memory on the host. > I suspect if you took all the DCD components of the current CXL device and repackaged it into a device called "DefinitelyNotACXLDCDDevice", that the CXL device inherited, this whole discussion goes away. Patches welcome? :] > > * Finding a tagged capacity devdax device in a VM should work the same as it > > does running on bare metal. > > Absolutely - that's a requirement. > > > * The file-backed (and devdax-backed) devdax abstraction is needed in qemu. > > Maybe. I'm not convinced the abstraction is needed at that particular level. > > > * Beyond that, I'm not yet sure what the lookup mechanism should be. Extra > > points for being easy to implement in both physical and virtual systems. > > For physical systems we aren't going to get agreement :( For the systems > I have visibility of there will be some diversity in hardware, but the > presentation to userspace and up consistency should be doable. > > Jonathan > > > > > Thanks for teeing this up! > > John > > > > > > [1] https://github.com/cxl-micron-reskit/famfs/blob/master/README.md > > > >