linux-kernel - Re: [PATCH 2/4] x86/bus_lock: Handle warn and fatal in #DB for bus lock

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Date:   Mon, 9 Nov 2020 09:29:58 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Tony Luck <tony.luck@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH 2/4] x86/bus_lock: Handle warn and fatal in #DB for bus
 lock

On Sun, Nov 08, 2020 at 04:29:16AM +0000, Fenghua Yu wrote:
> split_lock_detect=
> 		#AC for split lock		#DB for bus lock
> 
> off		Do nothing			Do nothing
> 
> warn		Kernel OOPs			Warn once per task and
> 		Warn once per task and		and continues to run.
> 		disable future checking 	When both features are
> 						supported, warn in #DB
> 
> fatal		Kernel OOPs			Send SIGBUS to user
> 		Send SIGBUS to user
> 		When both features are
> 		supported, fatal in #AC.

> +void handle_bus_lock(struct pt_regs *regs)
> +{
> +	if (!bld)
> +		return;
> +
> +	pr_warn_ratelimited("#DB: %s/%d took a bus_lock trap at address: 0x%lx\n",
> +			    current->comm, current->pid, regs->ip);
> +}

So the Changelog above, and the state_show() below, seem to suggest
there should be SIGBUS code in #DB, but I'm having trouble spotting it.

> +static void sld_state_show(void)
> +{
> +	if (!bld && !sld)
> +		return;
> +
> +	switch (sld_state) {
> +	case sld_off:
> +		pr_info("disabled\n");
> +		break;
> +
> +	case sld_warn:
> +		if (bld)
> +			pr_info("#DB: warning about user-space bus_locks\n");
> +		else
> +			pr_info("#AC: crashing the kernel about kernel split_locks and warning about user-space split_locks\n");
> +		break;
> +
> +	case sld_fatal:
> +		if (sld)
> +			pr_info("#AC: crashing the kernel on kernel split_locks and sending SIGBUS on user-space split_locks\n");
> +		else
> +			pr_info("#DB: sending SIGBUS on user-space bus_locks\n");
> +		break;
> +	}
> +}