Subject: Re: [PATCH] x86/mpx: Correctly report do_mpx_bt_fault() failures to
 user-space
To: Joerg Roedel <jroedel@suse.de>
References: <1491488362-27198-1-git-send-email-joro@8bytes.org>
 <0d387d7f-208e-75aa-55ea-0157412aa4d4@linux.intel.com>
 <20170420120801.GH5077@suse.de>
 <61c36474-63a5-d080-77d8-874e8c01c626@linux.intel.com>
 <20170421121901.GJ5077@suse.de>
Cc: Joerg Roedel <joro@8bytes.org>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, linux-kernel@vger.kernel.org
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <879ab29e-963f-4054-2767-74276fd1a3db@linux.intel.com>
Date: Fri, 21 Apr 2017 07:30:09 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101
 Thunderbird/45.5.1
MIME-Version: 1.0
In-Reply-To: <20170421121901.GJ5077@suse.de>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 815
Lines: 18

On 04/21/2017 05:19 AM, Joerg Roedel wrote:
> On Thu, Apr 20, 2017 at 08:45:28AM -0700, Dave Hansen wrote:
>> How about doing X86_TRAP_PF?  That would at least be consistent with
>> SIGBUS, which is probably the closest thing to a generic error code that
>> we have.
> Correct me if I am wrong, but for SIGBUS this only happens in the
> page-fault path, right? And this path is indeed entered on a #PF
> exception.

It can happen to programs for tons of reasons.  It definitely happens
outside page faults.

> I see no reason to lie to user-space about the trap_nr that caused the
> SIGSEGV, especially since user-space software needs to be modified to
> make use of MPX, including the signal handler. So there is no risk of
> introducing any incompatibility or regression, no?

I think it's pretty safe to change.