linux-kernel - Re: [PATCH v8 04/10] x86, mpx: hook #BR exception handler to allocate bound tables

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Message-ID: <54137A79.6060602@intel.com>
Date:	Fri, 12 Sep 2014 15:58:01 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Qiaowei Ren <qiaowei.ren@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
CC:	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 04/10] x86, mpx: hook #BR exception handler to allocate
 bound tables

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?

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