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

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Message-ID: <87o73ra0p7.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Fri, 11 Oct 2024 09:27:16 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: David Hildenbrand <david@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,  Ingo Molnar <mingo@...hat.com>,
  Borislav Petkov <bp@...en8.de>,  Dave Hansen
 <dave.hansen@...ux.intel.com>,  "Kirill A . Shutemov"
 <kirill.shutemov@...ux.intel.com>,  x86@...nel.org,
  linux-coco@...ts.linux.dev,  linux-mm@...ck.org,
  linux-kernel@...r.kernel.org,  Dan Williams <dan.j.williams@...el.com>,
  Kai Huang <kai.huang@...el.com>,  "H. Peter Anvin" <hpa@...or.com>,  Andy
 Lutomirski <luto@...nel.org>,  Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH -V2] tdx, memory hotplug: Check whole hot-adding memory
 range for TDX

David Hildenbrand <david@...hat.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.

$ grep __weak -r mm kernel init | wc -l
231

--
Best Regards,
Huang, Ying