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

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Message-ID: <21d0415c-9af4-db18-8e65-410f6ab5ec68@linux.intel.com>
Date:   Tue, 3 Nov 2020 20:15:27 +0800
From:   Xiaoyao Li <xiaoyao.li@...ux.intel.com>
To:     Fenghua Yu <fenghua.yu@...el.com>,
        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>
Cc:     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

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.


> +		handle_bus_lock(regs);
> +
>   	/* Add the virtual_dr6 bits for signals. */
>   	dr6 |= current->thread.virtual_dr6;
>   	if (dr6 & (DR_STEP | DR_TRAP_BITS) || icebp)
>