linux-kernel - Re: [PATCH RFC v3 2/4] x86/bus_lock: Handle warn and fatal in #DB for bus lock

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Date:   Fri, 6 Nov 2020 20:31:49 +0000
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Xiaoyao Li <xiaoyao.li@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Tony Luck <tony.luck@...el.com>,
        Christopherson Sean J <sean.j.christopherson@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH RFC v3 2/4] x86/bus_lock: Handle warn and fatal in #DB
 for bus lock

Hi, Xiaoyao,

On Tue, Nov 03, 2020 at 08:15:27PM +0800, Xiaoyao Li wrote:
> On 10/31/2020 8:27 AM, Fenghua Yu wrote:
> > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> > index 3c70fb34028b..1c3442000972 100644
> > --- a/arch/x86/kernel/traps.c
> > +++ b/arch/x86/kernel/traps.c
> > @@ -953,6 +953,13 @@ static __always_inline void exc_debug_user(struct pt_regs *regs,
> >   		goto out_irq;
> >   	}
> > +	/*
> > +	 * Handle bus lock. #DB for bus lock can only be triggered from
> > +	 * userspace.
> > +	 */
> > +	if (!(dr6 & DR_BUS_LOCK))
> 
> it should be
> 
> 	if (dr6 & DR_BUS_LOCK)
> 
> since you keep DR6.[bit 11] reserved in this version. bit 11 of
> debug_read_clear_dr6() being set to 1 means bus lock detected.

You are right. Will fix it in the next version.

Thank you very much!

-Fenghua