linux-kernel - Re: [PATCH v2] x86/mm: Hide mm_free_global_asid() definition under 'CONFIG_BROADCAST_TLB

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Message-ID: <20260116034722.GA104434@k08j02272.eu95sqa>
Date: Fri, 16 Jan 2026 11:47:22 +0800
From: Hou Wenlong <houwenlong.hwl@...group.com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, Rik van Riel <riel@...riel.com>,
	Thomas Gleixner <tglx@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Will Deacon <will@...nel.org>, Ryan Roberts <ryan.roberts@....com>,
	Jann Horn <jannh@...gle.com>, Barry Song <baohua@...nel.org>
Subject: Re: [PATCH v2] x86/mm: Hide mm_free_global_asid() definition under
 'CONFIG_BROADCAST_TLB_FLUSH'

On Thu, Jan 15, 2026 at 10:15:06AM +0100, Borislav Petkov wrote:
> On Thu, Jan 15, 2026 at 11:38:34AM +0800, Hou Wenlong wrote:
> > When 'CONFIG_BROADCAST_TLB_FLUSH' is not enabled, mm_free_global_asid()
> > remains a globally visible symbol and generates a useless function call
> > to it in destroy_context(). Therefore, hide the mm_free_global_asid()
> > definition under 'CONFIG_BROADCAST_TLB_FLUSH' and provide a static
> > inline empty version when it is not enabled to remove the function call.
> > 
> > Reviewed-by: Rik van Riel <riel@...riel.com>
> > Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
> > ---
> > v1->v2:
> > Keep the declarations of mm_init_global_asid() and mm_free_global_asid()
> > in 'asm/mmu_context.h' to fix the compilation failure of module
> > building.
> > ---
> >  arch/x86/include/asm/mmu_context.h | 2 --
> >  arch/x86/include/asm/tlbflush.h    | 3 +++
> >  arch/x86/mm/tlb.c                  | 4 ++--
> >  3 files changed, 5 insertions(+), 4 deletions(-)
> 
> Did you run the build tests I asked you to do before you sent this?
>

Honestly, I did not run all the tests you asked. I admit that my
attitude was somewhat hasty and not thorough. I sincerely apologize for
the trouble this has caused you and for taking up your time. After
testing the configuration you provided, I analyzed my code modifications
and noticed that the definition of 'mm_free_global_asid()' is included
under '#ifndef module' and is only called in destroy_context().
Therefore, I checked all the places where destroy_context() is called
and found that it is only called in 'kernel/fork.c', which is not invoked
in a module (and the original mm_free_global_asid() was not exported
either).  To save time, I only tested 'allyesconfig' and my test
configuration with module compilation under 'x86_64' and 'i386', and
since I did not encounter any issues, I went ahead and sent the patch. I
realize now that I did not conduct a complete set of tests.

Upon carefully comparing the configuration you provided, I found that
the GCC versions are different (mine is 12.2.0 and yours is 13.3.0), and
I am using the tip/master branch from the 12th, which also does not
match your '6.19-rc3'. After a full night of testing (using the tip/master
branch and the '6.19-rc5' tag), I still did not find any issues; it may be
related to the compiler. I will try using GCC 13.3.0 to see if that
makes a difference and will conduct more randconfig tests.

Finally, I apologize once again for taking up your time and thank you
for your kind reply.

Here is the script I used for testing:
```
# 64-bit
make clean
LOCALVERSION="" make allnoconfig
LOCALVERSION="" make -j32
make clean
LOCALVERSION="" make defconfig
LOCALVERSION="" make -j32
make clean
LOCALVERSION="" make allmodconfig
LOCALVERSION="" make -j32
make clean
LOCALVERSION="" make allyesconfig
LOCALVERSION="" make -j32

# 32-bit
make clean
LOCALVERSION="" make allnoconfig ARCH=i386
LOCALVERSION="" make -j32 ARCH=i386
make clean
LOCALVERSION="" make defconfig ARCH=i386
LOCALVERSION="" make -j32 ARCH=i386
make clean
LOCALVERSION="" make allmodconfig ARCH=i386
LOCALVERSION="" make -j32 ARCH=i386
make clean
LOCALVERSION="" make allyesconfig ARCH=i386
LOCALVERSION="" make -j32 ARCH=i386
```

Thanks!

> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette