Re: [PATCH -V2] tdx, memory hotplug: Check whole hot-adding memory range for TDX

["Huang, Ying" <ying.huang@intel.com>]

David Hildenbrand <david@redhat.com> writes:

> On 11.10.24 11:48, David Hildenbrand wrote:
>> On 11.10.24 10:51, Huang, Ying wrote:
>>> David Hildenbrand <david@redhat.com> writes:
>>>
>>>> On 11.10.24 03:27, Huang, Ying wrote:
>>>>> David Hildenbrand <david@redhat.com> writes:
>>>>>
>>>>>>>      extern u64 max_mem_size;
>>>>>>>        extern int mhp_online_type_from_str(const char *str);
>>>>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>>>>>> index 621ae1015106..c4769f24b1e2 100644
>>>>>>> --- a/mm/memory_hotplug.c
>>>>>>> +++ b/mm/memory_hotplug.c
>>>>>>> @@ -1305,6 +1305,11 @@ int try_online_node(int nid)
>>>>>>>      	return ret;
>>>>>>>      }
>>>>>>>      +int __weak arch_check_hotplug_memory_range(u64 start, u64 size)
>>>>>>> +{
>>>>>>> +	return 0;
>>>>>>> +}
>>>>>>
>>>>>> BTW, I remember that "__weak" doesn't always behave the way it would
>>>>>> seem, which is the reason we're usually using
>>>>>>
>>>>>> #define arch_check_hotplug_memory_range arch_check_hotplug_memory_range
>>>>>>
>>>>>> #ifndef arch_check_hotplug_memory_range
>>>>>> ...
>>>>>> #endif
>>>>>>
>>>>>>
>>>>>> Not that I remember the details, just that it can result in rather
>>>>>> surprising outcomes (e.g., the wrong function getting called).
>>>>> I can replace __weak with #define/#ifndef.
>>>>> However, it appears that "__weak" is still widely used now.
>>>>
>>>> Probably better to avoid new ones.
>>>
>>> Sure.  Will do that in the future versions.
>>>
>>>> See also
>>>> Documentation/dev-tools/checkpatch.rst
>>>>
>>>> I assume checkpatch.pl should complain as well?
>>>
>>> Double checked again.  It doesn't complain for that.
>> Indeed, it only checks for usage of "weak" for *declarations*. So
>> maybe
>> it's fine after all and I am misremembering things. So just leave it as
>> is for the time being.
>> 
>
> For completeness, this is the issue I remembered:
>
> commit 65d9a9a60fd71be964effb2e94747a6acb6e7015
> Author: Naveen N Rao <naveen@kernel.org>
> Date:   Fri Jul 1 13:04:04 2022 +0530
>
>     kexec_file: drop weak attribute from functions
>          As requested
>     (http://lkml.kernel.org/r/87ee0q7b92.fsf@email.froward.int.ebiederm.org),
>     this series converts weak functions in kexec to use the #ifdef approach.
>          Quoting the 3e35142ef99fe ("kexec_file: drop weak attribute
>         from
>     arch_kexec_apply_relocations[_add]") changelog:
>          : Since commit d1bcae833b32f1 ("ELF: Don't generate unused
>         section symbols")
>     : [1], binutils (v2.36+) started dropping section symbols that it thought
>     : were unused.  This isn't an issue in general, but with kexec_file.c, gcc
>     : is placing kexec_arch_apply_relocations[_add] into a separate
>     : .text.unlikely section and the section symbol ".text.unlikely" is being
>     : dropped.  Due to this, recordmcount is unable to find a non-weak symbol in
>     : .text.unlikely to generate a relocation record against.

Good to know this, Thanks!

--
Best Regards,
Huang, Ying