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Date: Fri, 12 Sep 2014 15:58:01 -0700
From: Dave Hansen <dave.hansen@intel.com>
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To: Qiaowei Ren <qiaowei.ren@intel.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>
CC: x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 04/10] x86, mpx: hook #BR exception handler to allocate
 bound tables
References: <1410425210-24789-1-git-send-email-qiaowei.ren@intel.com> <1410425210-24789-5-git-send-email-qiaowei.ren@intel.com>
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On 09/11/2014 01:46 AM, Qiaowei Ren wrote:
> +static int allocate_bt(long __user *bd_entry)
> +{
> +	unsigned long bt_addr, old_val = 0;
> +	int ret = 0;
> +
> +	bt_addr = mpx_mmap(MPX_BT_SIZE_BYTES);
> +	if (IS_ERR((void *)bt_addr))
> +		return bt_addr;
> +	bt_addr = (bt_addr & MPX_BT_ADDR_MASK) | MPX_BD_ENTRY_VALID_FLAG;

Qiaowei, why do we need the "& MPX_BT_ADDR_MASK" here?