linux-kernel - Re: [PATCH v3 4/8] x86/split_lock: Add and export split_lock_detect_enabled() and split_lock_detect

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Message-ID: <20200303185911.GR1439@linux.intel.com>
Date:   Tue, 3 Mar 2020 10:59:11 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, Paolo Bonzini <pbonzini@...hat.com>,
        Andy Lutomirski <luto@...nel.org>, tony.luck@...el.com,
        peterz@...radead.org, fenghua.yu@...el.com, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/8] x86/split_lock: Add and export
 split_lock_detect_enabled() and split_lock_detect_fatal()

On Thu, Feb 06, 2020 at 03:04:08PM +0800, Xiaoyao Li wrote:
> These two functions will be used by KVM to check whether host's
> sld_state.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
>  arch/x86/include/asm/cpu.h  |  4 ++++
>  arch/x86/kernel/cpu/intel.c | 12 ++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> index 2b20829db450..f5172dbd3f01 100644
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -46,6 +46,8 @@ unsigned int x86_stepping(unsigned int sig);
>  extern void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c);
>  extern void switch_to_sld(unsigned long tifn);
>  extern bool handle_user_split_lock(unsigned long ip);
> +extern bool split_lock_detect_enabled(void);
> +extern bool split_lock_detect_fatal(void);
>  #else
>  static inline void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) {}
>  static inline void switch_to_sld(unsigned long tifn) {}
> @@ -53,5 +55,7 @@ static inline bool handle_user_split_lock(unsigned long ip)
>  {
>  	return false;
>  }
> +static inline bool split_lock_detect_enabled(void) { return false; }
> +static inline bool split_lock_detect_fatal(void) { return false; }
>  #endif
>  #endif /* _ASM_X86_CPU_H */
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index ff27d026cb4a..b67b46ea66df 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -1131,3 +1131,15 @@ void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c)
>  	if (ia32_core_caps & MSR_IA32_CORE_CAPS_SPLIT_LOCK_DETECT)
>  		split_lock_setup();
>  }
> +
> +bool split_lock_detect_enabled(void)
> +{
> +	return sld_state != sld_off;
> +}
> +EXPORT_SYMBOL_GPL(split_lock_detect_enabled);

Hmm, ideally this would be static inline.  Patch 8 (to expose SLD to the
guest) queries this in vmx_vcpu_run(), I'd prefer to avoid the extra
CALL+RET in that path.

> +bool split_lock_detect_fatal(void)
> +{
> +	return sld_state == sld_fatal;
> +}
> +EXPORT_SYMBOL_GPL(split_lock_detect_fatal);

split_lock_detect_fatal() isn't used in this series, it shouldn't be added.

> -- 
> 2.23.0
>