linux-kernel - Re: [PATCH v2 1/8] x86/cpufeatures: Add Intel feature bits for Speculation Control

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Date:   Sun, 21 Jan 2018 11:17:13 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     David Woodhouse <dwmw@...zon.co.uk>
Cc:     arjan@...ux.intel.com, tglx@...utronix.de, karahmed@...zon.de,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com, bp@...en8.de, peterz@...radead.org,
        pbonzini@...hat.com, ak@...ux.intel.com,
        torvalds@...ux-foundation.org, gregkh@...ux-foundation.org
Subject: Re: [PATCH v2 1/8] x86/cpufeatures: Add Intel feature bits for
 Speculation Control


* David Woodhouse <dwmw@...zon.co.uk> wrote:

> Add three feature bits exposed by new microcode on Intel CPUs for
> speculation control. We would now be up to five bits in CPUID(7).RDX
> so take them out of the 'scattered' features and make a proper word
> for them instead as that leaf is a pure feature bits leaf.
> 
> [bp: heckle commitlog]
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Reviewed-by: Borislav Petkov <bp@...e.de>
> ---
>  arch/x86/include/asm/cpufeature.h        |  7 +++++--
>  arch/x86/include/asm/cpufeatures.h       | 12 +++++++++---
>  arch/x86/include/asm/disabled-features.h |  3 ++-
>  arch/x86/include/asm/required-features.h |  3 ++-
>  arch/x86/kernel/cpu/common.c             |  1 +
>  arch/x86/kernel/cpu/scattered.c          |  2 --
>  6 files changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index ea9a7dd..70eddb3 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -29,6 +29,7 @@ enum cpuid_leafs
>  	CPUID_8000_000A_EDX,
>  	CPUID_7_ECX,
>  	CPUID_8000_0007_EBX,
> +	CPUID_7_EDX,
>  };
>  
>  #ifdef CONFIG_X86_FEATURE_NAMES
> @@ -79,8 +80,9 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
>  	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 15, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 16, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 17, feature_bit) ||	\
> +	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 18, feature_bit) ||	\
>  	   REQUIRED_MASK_CHECK					  ||	\
> -	   BUILD_BUG_ON_ZERO(NCAPINTS != 18))
> +	   BUILD_BUG_ON_ZERO(NCAPINTS != 19))
>  
>  #define DISABLED_MASK_BIT_SET(feature_bit)				\
>  	 ( CHECK_BIT_IN_MASK_WORD(DISABLED_MASK,  0, feature_bit) ||	\
> @@ -101,8 +103,9 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 15, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 16, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 17, feature_bit) ||	\
> +	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 18, feature_bit) ||	\
>  	   DISABLED_MASK_CHECK					  ||	\
> -	   BUILD_BUG_ON_ZERO(NCAPINTS != 18))
> +	   BUILD_BUG_ON_ZERO(NCAPINTS != 19))
>  
>  #define cpu_has(c, bit)							\
>  	(__builtin_constant_p(bit) && REQUIRED_MASK_BIT_SET(bit) ? 1 :	\
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 25b9375..2efb8d4 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -13,7 +13,7 @@
>  /*
>   * Defines x86 CPU feature bits
>   */
> -#define NCAPINTS			18	   /* N 32-bit words worth of info */
> +#define NCAPINTS			19	   /* N 32-bit words worth of info */
>  #define NBUGINTS			1	   /* N 32-bit bug flags */
>  
>  /*
> @@ -206,8 +206,6 @@
>  #define X86_FEATURE_RETPOLINE		( 7*32+12) /* Generic Retpoline mitigation for Spectre variant 2 */
>  #define X86_FEATURE_RETPOLINE_AMD	( 7*32+13) /* AMD Retpoline mitigation for Spectre variant 2 */
>  #define X86_FEATURE_INTEL_PPIN		( 7*32+14) /* Intel Processor Inventory Number */
> -#define X86_FEATURE_AVX512_4VNNIW	( 7*32+16) /* AVX-512 Neural Network Instructions */
> -#define X86_FEATURE_AVX512_4FMAPS	( 7*32+17) /* AVX-512 Multiply Accumulation Single precision */
>  
>  #define X86_FEATURE_MBA			( 7*32+18) /* Memory Bandwidth Allocation */
>  #define X86_FEATURE_RSB_CTXSW		( 7*32+19) /* Fill RSB on context switches */
> @@ -319,6 +317,14 @@
>  #define X86_FEATURE_SUCCOR		(17*32+ 1) /* Uncorrectable error containment and recovery */
>  #define X86_FEATURE_SMCA		(17*32+ 3) /* Scalable MCA */
>  
> +/* Intel-defined CPU features, CPUID level 0x00000007:0 (EDX), word 18 */
> +#define X86_FEATURE_AVX512_4VNNIW	(18*32+ 2) /* AVX-512 Neural Network Instructions */
> +#define X86_FEATURE_AVX512_4FMAPS	(18*32+ 3) /* AVX-512 Multiply Accumulation Single precision */
> +#define X86_FEATURE_SPEC_CTRL		(18*32+26) /* Speculation Control (IBRS + IBPB) */
> +#define X86_FEATURE_STIBP		(18*32+27) /* Single Thread Indirect Branch Predictors */
> +#define X86_FEATURE_ARCH_CAPABILITIES	(18*32+29) /* IA32_ARCH_CAPABILITIES MSR (Intel) */

Ok, this patch should be split into at least two patches:

 - one extending the feature words from 18 to 19 and moving the two vector 
   computing feature bits

 - a separate one adding the speculation control bits

Thanks,

	Ingo