linux-kernel - Re: [PATCH v2 1/6] x86/split_lock: Add and export get_split_lock_detect

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Date:   Mon, 3 Feb 2020 13:45:24 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...capital.net>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Laight <David.Laight@...lab.com>
Subject: Re: [PATCH v2 1/6] x86/split_lock: Add and export
 get_split_lock_detect_state()

On Mon, Feb 03, 2020 at 11:16:03PM +0800, Xiaoyao Li wrote:
> get_split_lock_detect_state() will be used by KVM module to get sld_state.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
>  arch/x86/include/asm/cpu.h  | 12 ++++++++++++
>  arch/x86/kernel/cpu/intel.c | 12 ++++++------
>  2 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> index ff6f3ca649b3..167d0539e0ad 100644
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -40,11 +40,23 @@ int mwait_usable(const struct cpuinfo_x86 *);
>  unsigned int x86_family(unsigned int sig);
>  unsigned int x86_model(unsigned int sig);
>  unsigned int x86_stepping(unsigned int sig);
> +
> +enum split_lock_detect_state {
> +	sld_off = 0,
> +	sld_warn,
> +	sld_fatal,
> +};
> +
>  #ifdef CONFIG_CPU_SUP_INTEL
> +extern enum split_lock_detect_state get_split_lock_detect_state(void);
>  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(struct pt_regs *regs, long error_code);
>  #else
> +static inline enum split_lock_detect_state get_split_lock_detect_state(void)
> +{
> +	return sld_off;
> +}
>  static inline void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) {}
>  static inline void switch_to_sld(unsigned long tifn) {}
>  static inline bool handle_user_split_lock(struct pt_regs *regs, long error_code)
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index db3e745e5d47..a810cd022db5 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -33,12 +33,6 @@
>  #include <asm/apic.h>
>  #endif
>  
> -enum split_lock_detect_state {
> -	sld_off = 0,
> -	sld_warn,
> -	sld_fatal,
> -};
> -
>  /*
>   * Default to sld_off because most systems do not support split lock detection
>   * split_lock_setup() will switch this to sld_warn on systems that support
> @@ -968,6 +962,12 @@ cpu_dev_register(intel_cpu_dev);
>  #undef pr_fmt
>  #define pr_fmt(fmt) "x86/split lock detection: " fmt
>  
> +enum split_lock_detect_state get_split_lock_detect_state(void)
> +{
> +	return sld_state;
> +}
> +EXPORT_SYMBOL_GPL(get_split_lock_detect_state);

I'm pretty sure KVM doesn't need to differentiate between warn and fatal if
its #AC interceptor is routed through handle_user_split_lock().  I.e. this
can return a boolean without exporting the enum.

bool is_split_lock_detect_enabled(void)
{
	return sld_state != sld_off;
}

> +
>  static const struct {
>  	const char			*option;
>  	enum split_lock_detect_state	state;
> -- 
> 2.23.0
>