Unlike regular VMs, TDX guests use the firmware hand-off wakeup method to wake up the APs during the boot process. This wakeup model uses a mailbox to communicate with firmware to bring up the APs. As per the design, this mailbox can only be used once for the given AP, which means after the APs are booted, the same mailbox cannot be used to offline/online the given AP. More details about this requirement can be found in Intel TDX Virtual Firmware Design Guide, sec titled "AP initialization in OS" and in sec titled "Hotplug Device". Since the architecture does not support any method of offlining the CPUs, disable CPU hotplug support in the kernel. Since this hotplug disable feature can be re-used by other VM guests, add a new CC attribute CC_ATTR_HOTPLUG_DISABLED and use it to disable the hotplug support. Attempt to offline CPU will fail with -EOPNOTSUPP.
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| @@ -35,6 +35,7 @@ · 34 unmodified lines | ||
| 35 | 35 | #include <linux/percpu-rwsem.h> |
| 36 | 36 | #include <linux/cpuset.h> |
| 37 | 37 | #include <linux/random.h> |
| 38 | +#include <linux/cc_platform.h> | |
| 38 | 39 | |
| 39 | 40 | #include <trace/events/power.h> |
| 40 | 41 | #define CREATE_TRACE_POINTS |
| @@ -1186,6 +1187,12 @@ out: · 1145 unmodified lines | ||
| 1186 | 1187 | |
| 1187 | 1188 | static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target) |
| 1188 | 1189 | { |
| 1190 | + /* | |
| 1191 | + * If the platform does not support hotplug, report it explicitly to | |
| 1192 | + * differentiate it from a transient offlining failure. | |
| 1193 | + */ | |
| 1194 | + if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED)) | |
| 1195 | + return -EOPNOTSUPP; | |
| 1189 | 1196 | if (cpu_hotplug_disabled) |
| 1190 | 1197 | return -EBUSY; |
| 1191 | 1198 | return _cpu_down(cpu, 0, target); |