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The current hotplug (or dlpar) of devices (the process is generally the same for memory, cpu, and pci) on PowerVM systems is initiated from the HMC, which communicates the request to the partitions through the RSCT framework. The RSCT framework then invokes the drmgr command. The drmgr command performs the hotplug operation by doing some pieces, such as most of the rtas calls and device tree parsing, in userspace and make requests to the kernel to online/offline the device, update the device tree and add/remove the device. For PowerKVM the approach for device hotplug is to follow what is currently being done for pci hotplug. A hotplug request is initiated from the host. QEMU then generates an EPOW interrupt to the guest which causes the guest to make the rtas,check-exception call. In QEMU, the rtas,check-exception call returns a rtas hotplug event to the guest. Please note that the current pci hotplug path for PowerKVM involves the kernel receiving the rtas hotplug event, passing it to rtas_errd in userspace, and having rtas_errd invoke drmgr. The drmgr command then handles the request as described above for PowerVM systems. There is no need for this circuitous route, we should just handle the entire hotplug of devices in the kernel. What I am planning is to enable this by moving the code to handle hotplug from drmgr into the kernel to provide a single path for handling device hotplug for both PowerVM and PowerKVM systems. This patch provides the common iframework and entry point. For PowerKVM a future update to the kernel rtas code will recognize rtas hotplug events returned from rtas,check-exception calls and use the common entry point to handle hotplug of the device. For PowerVM systems, This patch creates /sys/kernel/dlpar that can be used by the drmgr command to initiate hotplug requests. In order to do this a string of the format "<resource> <action> <id_type> <id>" is written to this file. The string consists of a resource (cpu, memory, pci, phb), an action (add or remove), an id_type (count, drc index, drc name), and the corresponding id. The kernel will parse the string and create a rtas hotplug section that can be passed to the common entry point for handling hotplug requests. It should be noted that there is no chance of updating how we receive hotplug (dlpar) requests from the HMC on PowerVM systems. Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> |
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