linux-kernel - Re: [PATCH v2] x86/speculation: Use DECLARE_PER_CPU for x86_spec_ctrl

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Message-ID: <CAKwvOdkXdAXBTLipv5A3vaTe_dRPvtCDJobi=tHR9oSJab9oBw@mail.gmail.com>
Date:   Wed, 13 Jul 2022 08:36:16 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        stable@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2] x86/speculation: Use DECLARE_PER_CPU for x86_spec_ctrl_current

On Wed, Jul 13, 2022 at 8:25 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Clang warns:
>
>   arch/x86/kernel/cpu/bugs.c:58:21: error: section attribute is specified on redeclared variable [-Werror,-Wsection]
>   DEFINE_PER_CPU(u64, x86_spec_ctrl_current);
>                       ^
>   arch/x86/include/asm/nospec-branch.h:283:12: note: previous declaration is here
>   extern u64 x86_spec_ctrl_current;
>              ^
>   1 error generated.
>
> The declaration should be using DECLARE_PER_CPU instead so all
> attributes stay in sync.
>
> Cc: stable@...r.kernel.org
> Fixes: fc02735b14ff ("KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS")
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>
> v1 -> v2: https://lore.kernel.org/20220713152222.1697913-1-nathan@kernel.org/
>
> * Use asm/percpu.h instead of linux/percpu.h to avoid static call
>   include errors.
>
>  arch/x86/include/asm/nospec-branch.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> index bb05ed4f46bd..10a3bfc1eb23 100644
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -11,6 +11,7 @@
>  #include <asm/cpufeatures.h>
>  #include <asm/msr-index.h>
>  #include <asm/unwind_hints.h>
> +#include <asm/percpu.h>
>
>  #define RETPOLINE_THUNK_SIZE   32
>
> @@ -280,7 +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);
>
>
> base-commit: 72a8e05d4f66b5af7854df4490e3135168694b6b
> --
> 2.37.1
>
>


-- 
Thanks,
~Nick Desaulniers