Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image

[David Hildenbrand <david@redhat.com>]

On 24.04.20 09:39, David Hildenbrand wrote:
> On 23.04.20 18:29, Eric W. Biederman wrote:
>> David Hildenbrand <david@redhat.com> writes:
>>
>>>> The confusing part was talking about memory being still in use,
>>>> that is actually scheduled for use in the future.
>>>
>>> +1
>>>
>>>>
>>>>>> Usually somewhere in the loaded image
>>>>>> is a copy of the memory map at the time the kexec kernel was loaded.
>>>>>> That will invalidate the memory map as well.
>>>>>
>>>>> Ah, unconditionally. Sure, x86 needs this.
>>>>> (arm64 re-discovers the memory map from firmware tables after kexec)
>>>
>>> Does this include hotplugged DIMMs e.g., under KVM?
>>> [...]
>>
>> As far as I know.  If the memory map changes we need to drop the loaded
>> image.
>>
>>
>> Having thought about it a little more I suspect it would be the
>> other way and just block all hotplug actions after a kexec_load.
>> As all we expect to happen is running shutdown scripts.
>>
>> If blocking the hotplug action uses printk to print a nice message
>> saying something like: "Hotplug blocked because of a loaded kexec image",
>> then people will be able to figure out what is going on and
>> call kexec -u if they haven't started the shutdown scripts yet.
>>
>>
>> Either way it is something simple and unconditional that will make
>> things work.
>>
> 
> Personally, I consider memory hotplug more important than keeping loaded
> kexec data alive (just because somebody once decided to do a "kexec -l"
> and never did a "kexec -e" we should not block any memory hot(un)plug -
> especially in virtualized environments - for all eternity).
> 
> So IMHO we would invalidate loaded kexec data (not the crashkernel, of
> course) on memory hot(un)plug and print a warning. In addition, we can
> let kexec-tools try to reload whatever they loaded after getting
> notified that something changed.
> 
> The "something changed" is visible to user space e.g., via udev events
> for /sys/devices/memory/memoryX/

/sys/devices/system/memory/memoryX/ ...


-- 
Thanks,

David / dhildenb