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Tsirkin" , Vishal Verma , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Igor Mammedov , Paolo Bonzini , Dan Williams , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Ben Widawsky writes: > On 20-11-26 07:36:23, Markus Armbruster wrote: >> Ben Widawsky writes: >> >> > On 20-11-13 08:47:59, Markus Armbruster wrote: >> >> Eric Blake writes: >> >> >> >> > On 11/10/20 11:47 PM, Ben Widawsky wrote: >> >> >> A CXL memory device (AKA Type 3) is a CXL component that contains some >> >> >> combination of volatile and persistent memory. It also implements the >> >> >> previously defined mailbox interface as well as the memory device >> >> >> firmware interface. >> >> >> >> >> >> The following example will create a 256M device in a 512M window: >> >> >> >> >> >> -object "memory-backend-file,id=cxl-mem1,share,mem-path=cxl-type3,size=512M" >> >> >> -device "cxl-type3,bus=rp0,memdev=cxl-mem1,id=cxl-pmem0,size=256M" >> >> >> >> >> >> Signed-off-by: Ben Widawsky >> >> >> --- >> >> > >> >> >> +++ b/qapi/machine.json >> >> >> @@ -1394,6 +1394,7 @@ >> >> >> { 'union': 'MemoryDeviceInfo', >> >> >> 'data': { 'dimm': 'PCDIMMDeviceInfo', >> >> >> 'nvdimm': 'PCDIMMDeviceInfo', >> >> >> + 'cxl': 'PCDIMMDeviceInfo', >> >> >> 'virtio-pmem': 'VirtioPMEMDeviceInfo', >> >> >> 'virtio-mem': 'VirtioMEMDeviceInfo' >> >> >> } >> >> > >> >> > Missing documentation of the new data type, and the fact that it will be >> >> > introduced in 6.0. >> >> >> >> Old wish list item: improve the QAPI schema frontend to flag this. >> >> >> > >> > "Introduced in 6.0" - quite the optimist. Kidding aside, this is the area where >> > I could use some feedback. CXL Type 3 memory devices can contain both volatile >> > and persistent memory at the same time. As such, I think I'll need a new type to >> > represent that, but I'd love to know how best to accomplish that. >> >> We can help. Tell us what information you want to provide in variant >> 'cxl'. If it's a superset of an existing variant, give us just the >> delta. >> > > I'm not exactly sure what the best way to do this is in QEMU, so I'm not really > sure what to specify as the delta. A CXL memory device can have both volatile > and persistent memory. Currently when a CXL memory device implements the > TYPE_MEMORY_DEVICE interface. So I believe the shortest path is a > MemoryDeviceInfo that can have two memory devices associated with it, but I > don't know if that's the best path. Perhaps a CXL device should contain two sub-devices implementing TYPE_MEMORY_DEVICE. Paolo, what do you think? If yes, one of the existing variants fits the bill, I guess. If no, I have more ramblings to offer. query-memory-devices returns a MemoryDeviceInfo for each realized device that implements interface TYPE_MEMORY_DEVICE. The interface provides callback ->fill_device_info() to fill in the MemoryDeviceInfo. This is its only use. This means TYPE_MEMORY_DEVICE places no obvious constraints on how the callbacks use MemoryDeviceInfo. Each callback can pick whatever variant it wants. This also means *your* callback can pick a new one, which you define however you want. What if there are unobvious (and unwritten) constraints? The existing variants overlap: * All provide the device's ID: optional member @id * All provide a physical address (base address, I supposed) and size, but the member names differ (argh!): @addr, @size vs. @memaddr, @size * All provide the memory backend: member @memdev The members that overlap by necessity (i.e. any conceivable TYPE_MEMORY_DEVICE will have them) should be common members, not variant members. Requires converting the simple union to the equivalent flat union. Do these members overlap by necessity? Paolo, Igor? [...]