From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965117Ab1GOJHq (ORCPT ); Fri, 15 Jul 2011 05:07:46 -0400 Received: from gate.crashing.org ([63.228.1.57]:58016 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964982Ab1GOJHp (ORCPT ); Fri, 15 Jul 2011 05:07:45 -0400 Subject: Re: [PATCH 0/1] Fixup write permission of TLB on powerpc e500 core From: Benjamin Herrenschmidt To: MailingLists Cc: Peter Zijlstra , paulus@samba.org, tglx@linutronix.de, walken@google.com, dhowells@redhat.com, cmetcalf@tilera.com, tony.luck@intel.com, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org In-Reply-To: <4E1FFC7B.4000209@gmail.com> References: <1310717238-13857-1-git-send-email-haishan.bai@gmail.com> <1310718056.2586.275.camel@twins> <4E1FFC7B.4000209@gmail.com> Content-Type: text/plain; charset="UTF-8" Date: Fri, 15 Jul 2011 19:07:15 +1000 Message-ID: <1310720835.4968.311.camel@pasglop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2011-07-15 at 16:38 +0800, MailingLists wrote: > A page could be set to read only by the kernel (supervisor in the > powerpc > literature) on the e500, and that's what the kernel do. Set > SW(supervisor > write) bit in the TLB entry to grant write permission to the kernel on > a > page. > > And further the SW bit is set according to the DIRTY flag of the PTE, > PTE.DIRTY is set in the do_page_fault(), the futex_lock_pi() disabled > page fault, the PTE.DIRTY never can be set, so do the SW bit, > unbreakable > COW occurred, infinite loop followed. That would be it ... the SW dirty and young tracking relies on faults to fixup things in handle_pte_fault(). If the "disable page fault" thingy happens before we get there, then we have a pretty nasty bug. Note that this will hit more than just e500 (and in fact any architecture that relies on SW to do dirty and young tracking). Cheers, Ben.