Re: [PATCH v2 2/3] mm/memory_hotplug: Introduce MHP_NO_FIRMWARE_MEMMAP

David Hildenbrand
2020-05-02T09:26:58Z

>> Now, let's clarify what I want regarding virtio-mem:
>>
>> 1. kexec should not add virtio-mem memory to the initial firmware
>> memmap. The driver has to be in charge as discussed.
>> 2. kexec should not place kexec images onto virtio-mem memory. That
>> would end badly.
>> 3. kexec should still dump virtio-mem memory via kdump.
>
> Ok, but then seems to say to me that dax/kmem is a different type of
> (driver managed) than virtio-mem and it's confusing to try to apply
> the same meaning. Why not just call your type for the distinct type it
> is "System RAM (virtio-mem)" and let any other driver managed memory
> follow the same "System RAM ($driver)" format if it wants?

I had the same idea but discarded it because it seemed to uglify the
add_memory() interface (passing yet another parameter only relevant for
driver managed memory). Maybe we really want a new one, because I like
that idea:

/*
* Add special, driver-managed memory to the system as system ram.
* The resource_name is expected to have the name format "System RAM
* ($DRIVER)", so user space (esp. kexec-tools)" can special-case it.
*
* For this memory, no entries in /sys/firmware/memmap are created,
* as this memory won't be part of the raw firmware-provided memory map
* e.g., after a reboot. Also, the created memory resource is flagged
* with IORESOURCE_MEM_DRIVER_MANAGED, so in-kernel users can special-
* case this memory (e.g., not place kexec images onto it).
*/
int add_memory_driver_managed(int nid, u64 start, u64 size,
const char *resource_name);

If we'd ever have to special case it even more in the kernel, we could
allow to specify further resource flags. While passing the driver name
instead of the resource_name would be an option, this way we don't have
to hand craft new resource strings for added memory resources.

Thoughts?

--
Thanks,

David / dhildenb