linux-kernel - Re: [PATCH] x86: Fix static_key in load_mm

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Date:	Thu, 9 Jul 2015 15:11:30 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Ingo Molnar <mingo@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Vince Weaver <vince@...ter.net>,
	"hillf.zj" <hillf.zj@...baba-inc.com>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Fix static_key in load_mm_cr4()



On Thu, 9 Jul 2015, Peter Zijlstra wrote:

> 
> Mikulas reported his K6-3 not booting. This is because the static_key
> confusion struck and bit Andy, this wants to be static_key_false().
> 
> Fixes: a66734297f78 ("perf/x86: Add /sys/devices/cpu/rdpmc=2 to allow rdpmc for all tasks")
> Cc: Andy Lutomirski <luto@...capital.net>
> Reported-by: Mikulas Patocka <mpatocka@...hat.com>
> Tested-by: Mikulas Patocka <mpatocka@...hat.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>


You should also add
Cc: stable@...r.kernel.org	# v4.0
so that it will be backported to 4.0 and 4.1.

> ---
>  arch/x86/include/asm/mmu_context.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
> index 5e8daee7c5c9..804a3a6030ca 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -23,7 +23,7 @@ extern struct static_key rdpmc_always_available;
>  
>  static inline void load_mm_cr4(struct mm_struct *mm)
>  {
> -	if (static_key_true(&rdpmc_always_available) ||
> +	if (static_key_false(&rdpmc_always_available) ||
>  	    atomic_read(&mm->context.perf_rdpmc_allowed))
>  		cr4_set_bits(X86_CR4_PCE);
>  	else
> 
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