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SubjectRe: [PATCH v17] x86/split_lock: Enable split lock detection by kernel
On Sun, Jan 26, 2020 at 12:05:35PM -0800, Luck, Tony wrote:

...

> +bool handle_user_split_lock(struct pt_regs *regs, long error_code)

No reason to take the error code unless there's a plan to use it.

> +{
> + if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
> + return false;

Any objection to moving the EFLAGS.AC up to do_alignment_check()? And
take "unsigned long rip" instead of @regs?

That would allow KVM to reuse handle_user_split_lock() for guest faults
without any changes (other than exporting).

E.g. do_alignment_check() becomes:

if (!(regs->flags & X86_EFLAGS_AC) && handle_user_split_lock(regs->ip))
return;

> +
> + pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n",
> + current->comm, current->pid, regs->ip);
> +
> + /*
> + * Disable the split lock detection for this task so it can make
> + * progress and set TIF_SLD so the detection is re-enabled via
> + * switch_to_sld() when the task is scheduled out.
> + */
> + __sld_msr_set(false);
> + set_tsk_thread_flag(current, TIF_SLD);
> + return true;
> +}

...

> +dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code)
> +{
> + char *str = "alignment check";
> +
> + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
> +
> + if (notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_AC, SIGBUS) == NOTIFY_STOP)
> + return;
> +
> + if (!user_mode(regs))
> + die("Split lock detected\n", regs, error_code);
> +
> + local_irq_enable();
> +
> + if (handle_user_split_lock(regs, error_code))
> + return;
> +
> + do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs,
> + error_code, BUS_ADRALN, NULL);
> +}
> +
> #ifdef CONFIG_VMAP_STACK
> __visible void __noreturn handle_stack_overflow(const char *message,
> struct pt_regs *regs,
> --
> 2.21.1
>

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