Messages in this thread | | | Subject | Re: [PATCH v5 07/22] x86/virt/tdx: Implement SEAMCALL function | From | Kai Huang <> | Date | Wed, 03 Aug 2022 14:37:18 +1200 |
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On Thu, 2022-07-21 at 13:52 +1200, Kai Huang wrote: > Also, if I understand correctly above, your suggestion is we want to prevent any > CMR memory going offline so it won't be hot-removed (assuming we can get CMRs > during boot). This looks contradicts to the requirement of being able to allow > moving memory from core-mm to driver. When we offline the memory, we cannot > know whether the memory will be used by driver, or later hot-removed.
Hi Dave,
The high level flow of device hot-removal is:
acpi_scan_hot_remove() -> acpi_scan_try_to_offline() -> acpi_bus_offline() -> device_offline() -> memory_subsys_offline() -> acpi_bus_trim() -> acpi_memory_device_remove()
And memory_subsys_offline() can also be triggered via /sysfs:
echo 0 > /sys/devices/system/memory/memory30/online
After the memory block is offline, my understanding is kernel can theoretically move it to, i.e. ZONE_DEVICE via memremap_pages().
As you can see memory_subsys_offline() is the entry point of memory device offline (before it the code is generic for all ACPI device), and it cannot distinguish whether the removal is from ACPI event, or from /sysfs, so it seems we are unable to refuse to offline memory in memory_subsys_offline() when it is called from ACPI event.
Any comments?
-- Thanks, -Kai
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