On 30.09.24 07:51, Huang Ying wrote:
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.
ratelimiting would likely help here a lot, but I agree that it is suboptimal.
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.
> > The target use case is to support CXL memory on TDX enabled systems.
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.
I'm curious, why can that memory be used through devdax but not through the buddy? I'm probably missing something important :)
This also makes the original TDX memory hotplug notifier useless, so delete it.
The online-notifier would even be too late when used with the memmap-on-memory feature I assume, as we might be touching that memory even before being able to call memory online notifiers.
One way to handle that would be to switch to the MEM_PREPARE_ONLINE notifier, but it's still called per-memory block.
Nothing jumped at me, so Acked-by: David Hildenbrand <david@xxxxxxxxxx> -- Cheers, David / dhildenb
