linux-kernel - Re: [PATCH v2 12/15] x86/asm: Cleanup prefetch primitives

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Date:	Wed, 4 Mar 2015 07:48:48 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	X86 ML <x86@...nel.org>, Andy Lutomirski <luto@...capital.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 12/15] x86/asm: Cleanup prefetch primitives


* Borislav Petkov <bp@...en8.de> wrote:

> From: Borislav Petkov <bp@...e.de>
> 
> This is based on a patch originally by hpa.
> 
> With the current improvements to the alternatives, we can simply use %P1
> as a mem8 operand constraint and rely on the toolchain to generate the
> proper instruction sizes. For example, on 32-bit, where we use an empty
> old instruction we get:
> 
>   apply_alternatives: feat: 6*32+8, old: (c104648b, len: 4), repl: (c195566c, len: 4)
>   c104648b: alt_insn: 90 90 90 90
>   c195566c: rpl_insn: 0f 0d 4b 5c
> 
>   ...
> 
>   apply_alternatives: feat: 6*32+8, old: (c18e09b4, len: 3), repl: (c1955948, len: 3)
>   c18e09b4: alt_insn: 90 90 90
>   c1955948: rpl_insn: 0f 0d 08
> 
>   ...
> 
>   apply_alternatives: feat: 6*32+8, old: (c1190cf9, len: 7), repl: (c1955a79, len: 7)
>   c1190cf9: alt_insn: 90 90 90 90 90 90 90
>   c1955a79: rpl_insn: 0f 0d 0d a0 d4 85 c1
> 
> all with the proper padding done depending on the size of the
> replacement instruction the compiler generates.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Cc: H. Peter Anvin <hpa@...ux.intel.com>
> ---
>  arch/x86/include/asm/apic.h      |  2 +-
>  arch/x86/include/asm/processor.h | 16 +++++++---------
>  arch/x86/kernel/cpu/amd.c        |  5 +++++
>  3 files changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index efc3b22d896e..8118e94d50ab 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -91,7 +91,7 @@ static inline void native_apic_mem_write(u32 reg, u32 v)
>  {
>  	volatile u32 *addr = (volatile u32 *)(APIC_BASE + reg);
>  
> -	alternative_io("movl %0, %1", "xchgl %0, %1", X86_BUG_11AP,
> +	alternative_io("movl %0, %P1", "xchgl %0, %P1", X86_BUG_11AP,
>  		       ASM_OUTPUT2("=r" (v), "=m" (*addr)),
>  		       ASM_OUTPUT2("0" (v), "m" (*addr)));
>  }
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index ec1c93588cef..7be2c9a6caba 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -761,10 +761,10 @@ extern char			ignore_fpu_irq;
>  #define ARCH_HAS_SPINLOCK_PREFETCH
>  
>  #ifdef CONFIG_X86_32
> -# define BASE_PREFETCH		ASM_NOP4
> +# define BASE_PREFETCH		""
>  # define ARCH_HAS_PREFETCH
>  #else
> -# define BASE_PREFETCH		"prefetcht0 (%1)"
> +# define BASE_PREFETCH		"prefetcht0 %P1"
>  #endif
>  
>  /*
> @@ -775,10 +775,9 @@ extern char			ignore_fpu_irq;
>   */
>  static inline void prefetch(const void *x)
>  {
> -	alternative_input(BASE_PREFETCH,
> -			  "prefetchnta (%1)",
> +	alternative_input(BASE_PREFETCH, "prefetchnta %P1",
>  			  X86_FEATURE_XMM,
> -			  "r" (x));
> +			  "m" (*(const char *)x));
>  }
>  
>  /*
> @@ -788,10 +787,9 @@ static inline void prefetch(const void *x)
>   */
>  static inline void prefetchw(const void *x)
>  {
> -	alternative_input(BASE_PREFETCH,
> -			  "prefetchw (%1)",
> -			  X86_FEATURE_3DNOW,
> -			  "r" (x));
> +	alternative_input(BASE_PREFETCH, "prefetchw %P1",
> +			  X86_FEATURE_3DNOWPREFETCH,
> +			  "m" (*(const char *)x));
>  }
>  
>  static inline void spin_lock_prefetch(const void *x)
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index a220239cea65..dd9e50500297 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -711,6 +711,11 @@ static void init_amd(struct cpuinfo_x86 *c)
>  		set_cpu_bug(c, X86_BUG_AMD_APIC_C1E);
>  
>  	rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
> +
> +	/* 3DNow or LM implies PREFETCHW */
> +	if (!cpu_has(c, X86_FEATURE_3DNOWPREFETCH))
> +		if (cpu_has(c, X86_FEATURE_3DNOW) || cpu_has(c, X86_FEATURE_LM))
> +			set_cpu_cap(c, X86_FEATURE_3DNOWPREFETCH);
>  }
>  

For future reference: you forgot to declare the cpu/amd.c 
X86_FEATURE_3DNOWPREFETCH enablement change in the changelog.
I guess you noticed it during testing and forgot about it?

Thanks,

	Ingo
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