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

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Message-ID: <52f0c74cb1714a78bc84e158d26e7c38@intel.com>
Date:   Tue, 10 Nov 2020 21:51:21 +0000
From:   "Yu, Fenghua" <fenghua.yu@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Randy Dunlap" <rdunlap@...radead.org>,
        "Li, Xiaoyao" <xiaoyao.li@...el.com>,
        "Shankar, Ravi V" <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

Hi, Peter,

> 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.

You are right. The SIGBUS is missing here. Somehow my tests didn't capture the issue.

I will add:
+		force_sig_fault(SIGBUS, BUS_ADRALN, NULL);
to send SIGBUS in fatal case for #DB bus lock.

Thank you very much for your review!

-Fenghua