On 30.04.20 17:38, Eric W. Biederman wrote:

David Hildenbrand [off-list ref] writes:

quoted

Some devices/drivers that add memory via add_memory() and friends (e.g.,
dax/kmem, but also virtio-mem in the future) don't want to create entries
in /sys/firmware/memmap/ - primarily to hinder kexec from adding this
memory to the boot memmap of the kexec kernel.

In fact, such memory is never exposed via the firmware memmap as System
RAM (e.g., e820), so exposing this memory via /sys/firmware/memmap/ is
wrong:
 "kexec needs the raw firmware-provided memory map to setup the
  parameter segment of the kernel that should be booted with
  kexec. Also, the raw memory map is useful for debugging. For
  that reason, /sys/firmware/memmap is an interface that provides
  the raw memory map to userspace." [1]

We don't have to worry about firmware_map_remove() on the removal path.
If there is no entry, it will simply return with -EINVAL.

[1]
https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-firmware-memmap

You know what this justification is rubbish, and I have previously
explained why it is rubbish.

Actually, no, I don't think it is rubbish. See patch #3 and the cover
letter why this is the right thing to do *for special memory*, *not
ordinary DIMMs*.

And to be quite honest, I think your response is a little harsh. I don't
recall you replying to my virtio-mem-related comments.

Nacked-by: "Eric W. Biederman" [off-list ref]

This needs to be based on weather the added memory is ultimately normal
ram or is something special.

Yes, that's what the caller are expected to decide, see patch #3.

kexec should try to be as closely as possible to a real reboot - IMHO.

At least when we are talking memory resources.  Keeping it out of the
firmware map that is fine.

If the hotplugged memory is the result of plugging a stick of ram
into the kernel and can and should used be like any other memory
it should be treated like any normal memory.

If the hotplugged memory is something special it should be treated as
something special.

I am really sorry, I can't make sense of what you are trying to say here.

Justifying behavior by documentation that does not consider memory
hotplug is bad thinking.

Are you maybe confusing this patch series with the arm64 approach? This
is not about ordinary hotplugged DIMMs.

I'd love to get Dan's, Dave's and Michal's opinion.

-- 
Thanks,

David / dhildenb