linux-kernel - Re: [PATCH v5 4/9] x86/split_lock: Export handle_user_split

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Date:   Fri, 20 Mar 2020 17:48:09 -0700
From:   "Luck, Tony" <tony.luck@...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>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v5 4/9] x86/split_lock: Export handle_user_split_lock()

On Sun, Mar 15, 2020 at 01:05:12PM +0800, Xiaoyao Li wrote:
> In the future, KVM will use handle_user_split_lock() to handle #AC
> caused by split lock in guest. Due to the fact that KVM doesn't have
> a @regs context and will pre-check EFLASG.AC, move the EFLAGS.AC check
> to do_alignment_check().
> 
> Suggested-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
>  arch/x86/include/asm/cpu.h  | 4 ++--
>  arch/x86/kernel/cpu/intel.c | 7 ++++---
>  arch/x86/kernel/traps.c     | 2 +-
>  3 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> index ff6f3ca649b3..ff567afa6ee1 100644
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -43,11 +43,11 @@ unsigned int x86_stepping(unsigned int sig);
>  #ifdef CONFIG_CPU_SUP_INTEL
>  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);
> +extern bool handle_user_split_lock(unsigned long ip);
>  #else
>  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)
> +static inline bool handle_user_split_lock(unsigned long ip)
>  {
>  	return false;
>  }
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index 3eeab717a0d0..c401d174c8db 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -1102,13 +1102,13 @@ static void split_lock_init(struct cpuinfo_x86 *c)
>  	sld_state = sld_disable;
>  }
>  
> -bool handle_user_split_lock(struct pt_regs *regs, long error_code)
> +bool handle_user_split_lock(unsigned long ip)
>  {
> -	if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
> +	if (sld_state == sld_fatal)
>  		return false;
>  
>  	pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n",
> -			    current->comm, current->pid, regs->ip);
> +			    current->comm, current->pid, ip);
>  
>  	/*
>  	 * Disable the split lock detection for this task so it can make
> @@ -1119,6 +1119,7 @@ bool handle_user_split_lock(struct pt_regs *regs, long error_code)
>  	set_tsk_thread_flag(current, TIF_SLD);
>  	return true;
>  }
> +EXPORT_SYMBOL_GPL(handle_user_split_lock);
>  
>  /*
>   * This function is called only when switching between tasks with
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 0ef5befaed7d..407ff9be610f 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -304,7 +304,7 @@ dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code)
>  
>  	local_irq_enable();
>  
> -	if (handle_user_split_lock(regs, error_code))
> +	if (!(regs->flags & X86_EFLAGS_AC) && handle_user_split_lock(regs->ip))
>  		return;
>  
>  	do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs,
> -- 
> 2.20.1
> 

Looks good to me.

Reviewed-by: Tony Luck <tony.luck@...el.com>