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

[David Hildenbrand]

On 11.10.24 11:48, David Hildenbrand wrote:
> On 11.10.24 10:51, Huang, Ying wrote:
> > David Hildenbrand <david@xxxxxxxxxx> writes:
> >
> > > On 11.10.24 03:27, Huang, Ying wrote:
> > > > David Hildenbrand <david@xxxxxxxxxx> 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@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx),
    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.



--
Cheers,

David / dhildenb