linux-kernel - Re: [PATCH 29/35] x86/speculation: Add IPBP support

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Date:   Thu, 18 Jan 2018 19:31:16 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH 29/35] x86/speculation: Add IPBP support

On Thu, Jan 18, 2018 at 02:48:29PM +0100, Peter Zijlstra wrote:
> From: Thomas Gleixner <tglx@...utronix.de>

<--- Add commit message here.

> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/x86/include/asm/cpufeatures.h   |    4 +++-
>  arch/x86/include/asm/msr-index.h     |    3 +++
>  arch/x86/include/asm/nospec-branch.h |    9 +++++++++
>  arch/x86/kernel/cpu/bugs.c           |    2 ++
>  arch/x86/kernel/cpu/specctrl.c       |    9 +++++++++
>  5 files changed, 26 insertions(+), 1 deletion(-)
> 
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -212,8 +212,9 @@
>  
>  #define X86_FEATURE_MBA			( 7*32+18) /* Memory Bandwidth Allocation */
>  #define X86_FEATURE_RSB_CTXSW		( 7*32+19) /* Fill RSB on context switches */
> -#define X86_FEATURE_SPEC_CTRL		( 7*32+20) /* Speculation Control */
> +#define X86_FEATURE_SPEC_CTRL		( 7*32+20) /* Speculation Control - Intel only */
>  #define X86_FEATURE_IBRS		( 7*32+21) /* Indirect Branch Restricted Speculation */
> +#define X86_FEATURE_IBPB		( 7*32+22) /* Indirect Branch Prediction Barrier */
>  
>  /* Virtualization flags: Linux defined, word 8 */
>  #define X86_FEATURE_TPR_SHADOW		( 8*32+ 0) /* Intel TPR Shadow */
> @@ -273,6 +274,7 @@
>  #define X86_FEATURE_CLZERO		(13*32+ 0) /* CLZERO instruction */
>  #define X86_FEATURE_IRPERF		(13*32+ 1) /* Instructions Retired Count */
>  #define X86_FEATURE_XSAVEERPTR		(13*32+ 2) /* Always save/restore FP error pointers */
> +#define X86_FEATURE_AMD_IBPB		(13*32+12) /* Indirect Branch Prediction Barrier support */

I guess you could make that

#define X86_FEATURE_AMD_IBPB		(13*32+12) /* "" Indirect Branch Prediction Barrier support */

(note the "" in the comment)

so that it doesn't appear in /proc/cpuinfo as those two flags denote the
same thing.

>  /* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */
>  #define X86_FEATURE_DTHERM		(14*32+ 0) /* Digital Thermal Sensor */
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -46,6 +46,9 @@
>  #define SPEC_CTRL_DISABLE_IBRS		(0 << 0)
>  #define SPEC_CTRL_ENABLE_IBRS		(1 << 0)
>  
> +#define MSR_IA32_PRED_CMD		0x00000049
> +#define PRED_CMD_IBPB			(1 << 0)
> +
>  #define MSR_IA32_PERFCTR0		0x000000c1
>  #define MSR_IA32_PERFCTR1		0x000000c2
>  #define MSR_FSB_FREQ			0x000000cd
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -231,5 +231,14 @@ static inline void restart_indirect_bran
>  	if (static_cpu_has(X86_FEATURE_IBRS))
>  		native_wrmsrl(MSR_IA32_SPEC_CTRL, SPEC_CTRL_DISABLE_IBRS);
>  }
> +
> +void specctrl_init_ibpb(void);
> +
> +static inline void indirect_branch_prediction_barrier(void)

That's a long name: ibp_barrier() is what I had called it, with a
comment above it.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.