Re: [linux-stable-rc:linux-5.10.y 7109/7120] arch/x86/kernel/cpu/bugs.c:57:21: warning: section attribute is specified on redeclared variable

[Nathan Chancellor]

On Tue, Jul 12, 2022 at 01:21:15PM -0700, Nathan Chancellor wrote:
> On Wed, Jul 13, 2022 at 04:07:25AM +0800, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-5.10.y
> > head:   ba398a0e54049bb6a1c102245ae84103f103ff2c
> > commit: 855b78ccf1c8c952e148bdbd234cde117b098060 [7109/7120] KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS
> > config: i386-randconfig-a013 (https://download.01.org/0day-ci/archive/20220713/202207130344.AUqExE4E-lkp@xxxxxxxxx/config)
> > compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project badda4ac3c489a8c8cccdad1f74b9308c350a9e0)
> > reproduce (this is a W=1 build):
> >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         # https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/commit/?id=855b78ccf1c8c952e148bdbd234cde117b098060
> >         git remote add linux-stable-rc https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
> >         git fetch --no-tags linux-stable-rc linux-5.10.y
> >         git checkout 855b78ccf1c8c952e148bdbd234cde117b098060
> >         # save the config file
> >         mkdir build_dir && cp config build_dir/.config
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash arch/x86/kernel/
> > 
> > If you fix the issue, kindly add following tag where applicable
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > 
> > All warnings (new ones prefixed by >>):
> > 
> > >> arch/x86/kernel/cpu/bugs.c:57:21: warning: section attribute is specified on redeclared variable [-Wsection]
> >    DEFINE_PER_CPU(u64, x86_spec_ctrl_current);
> >                        ^
> >    arch/x86/include/asm/nospec-branch.h:278:12: note: previous declaration is here
> >    extern u64 x86_spec_ctrl_current;
> >               ^
> >    1 warning generated.
> > 
> > 
> > vim +57 arch/x86/kernel/cpu/bugs.c
> > 
> > c40221c4c496c5 Peter Zijlstra 2022-06-14  55  
> > c40221c4c496c5 Peter Zijlstra 2022-06-14  56  /* The current value of the SPEC_CTRL MSR with task-specific bits set */
> > c40221c4c496c5 Peter Zijlstra 2022-06-14 @57  DEFINE_PER_CPU(u64, x86_spec_ctrl_current);
> > c40221c4c496c5 Peter Zijlstra 2022-06-14  58  EXPORT_SYMBOL_GPL(x86_spec_ctrl_current);
> > c40221c4c496c5 Peter Zijlstra 2022-06-14  59  
> > 
> > :::::: The code at line 57 was first introduced by commit
> > :::::: c40221c4c496c5c026ede111094a96f292875d88 x86/bugs: Keep a per-CPU IA32_SPEC_CTRL value
> > 
> > :::::: TO: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > :::::: CC: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > 
> > -- 
> > 0-DAY CI Kernel Test Service
> > https://01.org/lkp
> > 
> 
> Looks like that declaration should be using DECLARE_PER_CPU?

Additionally, this appears to be an issue on mainline, our CI is
starting to roll in with these patches (clang-13 + x86_64 allmodconfig):

https://github.com/ClangBuiltLinux/continuous-integration2/actions/runs/2658541992

https://builds.tuxbuild.com/2Br2Q4juY6VKxbmgzULKe5C3pGq/build.log

I am happy to send a patch if this is correct, unless someone else wants
to.

> Cheers,
> Nathan
> 
> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> index 2989b42fcf4e..cbd56675bd7e 100644
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -281,7 +281,7 @@ static inline void indirect_branch_prediction_barrier(void)
>  
>  /* The Intel SPEC CTRL MSR base value cache */
>  extern u64 x86_spec_ctrl_base;
> -extern u64 x86_spec_ctrl_current;
> +DECLARE_PER_CPU(u64, x86_spec_ctrl_current);
>  extern void write_spec_ctrl_current(u64 val, bool force);
>  extern u64 spec_ctrl_current(void);
>  
>