On systems with TDX (Trust Domain eXtensions) enabled, memory ranges
hot-added must be checked for compatibility by TDX. This is currently
implemented through memory hotplug notifiers for each memory_block.
If a memory range which isn't TDX compatible is hot-added, for
example, some CXL memory, the command line as follows,
$ echo 1 > /sys/devices/system/node/nodeX/memoryY/online
will report something like,
bash: echo: write error: Operation not permitted
If pr_debug() is enabled, the error message like below will be shown
in the kernel log,
online_pages [mem 0xXXXXXXXXXX-0xXXXXXXXXXX] failed
Both are too general to root cause the problem. This will confuse
users. One solution is to print some error messages in the TDX memory
hotplug notifier. However, memory hotplug notifiers are called for
each memory block, so this may lead to a large volume of messages in
the kernel log if a large number of memory blocks are onlined with a
script or automatically. For example, the typical size of memory
block is 128MB on x86_64, when online 64GB CXL memory, 512 messages
will be logged.
> > The target use case is to support CXL memory on TDX enabled systems.
Therefore, in this patch, the whole hot-adding memory range is checked
for TDX compatibility through a newly added architecture specific
function (arch_check_hotplug_memory_range()). If rejected, the memory
hot-adding will be aborted with a proper kernel log message. Which
looks like something as below,
virt/tdx: Reject hot-adding memory range: 0xXXXXXXXX-0xXXXXXXXX for TDX compatibility.
If the CXL memory isn't compatible with TDX, the whole CXL memory
range hot-adding will be rejected. While the CXL memory can still be
used via devdax interface.
This also makes the original TDX memory hotplug notifier useless, so
delete it.