From mboxrd@z Thu Jan  1 00:00:00 1970
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: Generic page fault (Was: libsigsegv ....)
Date: Sun, 01 Mar 2015 09:49:39 +1100
Message-ID: <1425163779.4645.151.camel@kernel.crashing.org>
References: <1422361485.6648.71.camel@opensuse.org>
	 <54C78756.9090605@suse.cz>
	 <alpine.LSU.2.11.1501271347440.30227@nerf60.vanv.qr>
	 <1422364084.6648.82.camel@opensuse.org> <s5h7fw8hvdp.wl-tiwai@suse.de>
	 <CA+55aFyzy_wYHHnr2gDcYr7qcgOKM2557bRdg6RBa=cxrynd+Q@mail.gmail.com>
	 <CA+55aFxRnj97rpSQvvzLJhpo7C8TQ-F=eB1Ry2n53AV1rN8mwA@mail.gmail.com>
	 <CAMo8BfLsKCV_2NfgMH4k9jGOHs_-3=NKjCD3o3KK1uH23-6RRg@mail.gmail.com>
	 <CA+55aFzQ5QEZ1AYauWviq1gp5j=mqByAtt4fpteeK7amuxcyjw@mail.gmail.com>
	 <1422836637.17302.9.camel@au1.ibm.com>
	 <CA+55aFw9sg7pu9-2RbMGyPv5yUtcH54QowoH+5RhWqpPYg4YGQ@mail.gmail.com>
	 <1425107567.4645.108.camel@kernel.crashing.org>
	 <CA+55aFy5UvzSgOMKq09u4psz5twtC4aowuK6tofGKDEu-KFMJQ@mail.gmail.com>
	 <1425158083.4645.139.camel@kernel.crashing.org>
	 <CA+55aFzLQWZJR+Y8HAhdPDSiL0QH_Lx2BqPkiFckAO69bJcOtA@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Return-path: <linux-arch-owner@vger.kernel.org>
Received: from gate.crashing.org ([63.228.1.57]:45137 "EHLO gate.crashing.org"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751434AbbB1Wts (ORCPT <rfc822;linux-arch@vger.kernel.org>);
	Sat, 28 Feb 2015 17:49:48 -0500
In-Reply-To: <CA+55aFzLQWZJR+Y8HAhdPDSiL0QH_Lx2BqPkiFckAO69bJcOtA@mail.gmail.com>
Sender: linux-arch-owner@vger.kernel.org
List-ID: <linux-arch.vger.kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>

On Sat, 2015-02-28 at 13:49 -0800, Linus Torvalds wrote:

 .../...

>  - we handle write faults separately (see the first part of access_error()
> 
>  - so now we know it was a read or an instruction fetch
> 
>  - if PF_PROT is set, that means that the present bit was set in the
> page tables, so it must have been an exec access to a NX page
> 
>  - otherwise, we just say "PROTNONE means no access, otherwise
> populate the page tables"
> 
> .. and if it turns out that it was a PF_INSTR to a NX page, we'll end
> up taking the page fault *again* after it's been populated, and now
> since the page table was populated, the access_error() will catch it
> with the PF_PROT case.
> 
> Or something like that. I might have screwed up some detail, but it
> should all work.

I see, it should work yes, I'll still add that FAULT_FLAG_EXEC for
those who can tell reliably but it shouldn't hurt for x86 to not set it.

Cheers,
Ben.


>                      Linus
> --
> To unsubscribe from this list: send the line "unsubscribe linux-arch" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html