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

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Message-ID: <71dc3853-45a6-4fa5-b3c6-b165e0ab6a1b@redhat.com>
Date: Fri, 11 Oct 2024 09:53:10 +0200
From: David Hildenbrand <david@...hat.com>
To: "Huang, Ying" <ying.huang@...el.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

On 11.10.24 03:27, Huang, Ying wrote:
> 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.

Probably better to avoid new ones. See also 
Documentation/dev-tools/checkpatch.rst

I assume checkpatch.pl should complain as well?

-- 
Cheers,

David / dhildenb