Re: [RFC PATCH v3 21/31] hw/cxl/device: Add a memory device (8.2.8.5)

Eric Blake
2021-02-02T14:29:12Z

On 2/1/21 6:59 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.
>
> Although the memory device is configured like a normal PCIe device, the
> memory traffic is on an entirely separate bus conceptually (using the
> same physical wires as PCIe, but different protocol).
>
> The guest physical address for the memory device is part of a larger
> window which is owned by the platform. Currently, this is hardcoded as
> an object property on host bridge (PXB) creation, but that will need to
> change for interleaving.
>
> 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 <ben.widawsky@intel.com>
> ---

> +++ 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 that 'cxl' was introduced in 6.0. Also, is it
worth keeping the branches of this union in lexicographic order?

--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org