Re: [PATCH v3 1/8] x86/split_lock: Export handle_user_split_lock()

Sean Christopherson
2020-03-03T18:42:12Z

On Thu, Feb 06, 2020 at 03:04:05PM +0800, Xiaoyao Li wrote:
> Move the EFLAGS.AC check to do_alignment_check() so that
> handle_user_split_lock() can be used by KVM in the future to handle #AC
> caused by split lock in guest.

Probably worth explaining that KVM doesn't have a @regs context and will
pre-check EFLAGS.AC.

> Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.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 db3e745e5d47..2b3874a96bd4 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -1058,13 +1058,13 @@ static void split_lock_init(void)
> sld_state = sld_off;
> }
>
> -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
> @@ -1075,6 +1075,7 @@ 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,
> --
> 2.23.0
>