linux-kernel - Re: [PATCH v4 2/3] x86, mpx: hook #BR exception handler to allocate bound tables

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Message-ID: <52FBD74F.7050203@mit.edu>
Date:	Wed, 12 Feb 2014 12:19:27 -0800
From:	Andy Lutomirski <luto@...capital.net>
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-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] x86, mpx: hook #BR exception handler to allocate
 bound tables

On 02/12/2014 10:36 AM, Qiaowei Ren wrote:
> An access to an invalid bound directory entry will cause a #BR
> exception. This patch hook #BR exception handler to allocate
> one bound table and bind it with that buond directory entry.
> 
> This will avoid the need of forwarding the #BR exception
> to the user space when bound directory has invalid entry.
> 
> Signed-off-by: Qiaowei Ren <qiaowei.ren@...el.com>
> ---
> +void do_mpx_bt_fault(struct xsave_struct *xsave_buf)
> +{
> +	unsigned long status;
> +	unsigned long bd_entry, bd_base;
> +	unsigned long bd_size = 1UL << (MPX_L1_BITS+MPX_L1_SHIFT);
> +
> +	bd_base = xsave_buf->bndcsr.cfg_reg_u & MPX_BNDCFG_ADDR_MASK;
> +	status = xsave_buf->bndcsr.status_reg;
> +
> +	bd_entry = status & MPX_BNDSTA_ADDR_MASK;
> +	if ((bd_entry >= bd_base) && (bd_entry < bd_base + bd_size))
> +		allocate_bt(bd_entry);
> +}

This still just loops on failure, right?

--Andy
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