From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v1 3/6] x86: Enable Supervisor Mode
 Execution Prevention (SMAP) for Xen
Date: Tue, 15 Apr 2014 15:00:39 +0100
Message-ID: <534D3B87.7030109@citrix.com>
References: <1397566907-19710-1-git-send-email-feng.wu@intel.com>
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To: Feng Wu <feng.wu@intel.com>
Cc: jun.nakajima@intel.com, eddie.dong@intel.com, Ian.Campbell@citrix.com, JBeulich@suse.com, xen-devel@lists.xen.org
List-Id: xen-devel@lists.xenproject.org

On 15/04/14 14:01, Feng Wu wrote:
> @@ -1379,8 +1396,8 @@ void do_page_fault(struct cpu_user_regs *regs)
>  
>      if ( unlikely(!guest_mode(regs)) )
>      {
> -        pf_type = spurious_page_fault(addr, error_code);
> -        BUG_ON(pf_type == smep_fault);
> +        pf_type = spurious_page_fault(addr, regs);
> +        BUG_ON((pf_type == smep_fault) || (pf_type == smap_fault));

On further consideration, given the nature of faults like these, this
code would be better as:

if ( (pf_type == smep_fault) || (pf_type == smap_fault) )
{
    console_start_sync();
    printk("Xen SM%cP violation", pf_type == smep_fault ? 'E' : 'A');
    fatal_trap(TRAP_page_fault, regs);
}

This would make the resulting crash crystal clear as to what went wrong,
and forgo the first step of having to look up which BUG() tripped.

~Andrew