From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: Is: [PATCH] x86/paravirt: PTE updates in k(un)map_atomic need to be synchronous, regardless of lazy_mmu mode. Was: Re: [PATCH] x86/paravirt: Partially revert "remove lazy mode in interrupts" Date: Mon, 3 Oct 2011 13:04:01 -0400 Message-ID: <20111003170401.GD4420@phenom.oracle.com> References: <1317042797-19975-1-git-send-email-konrad.wilk@oracle.com> <4E80A6BD.3070703@goop.org> <20110926193453.GA9717@phenom.oracle.com> <4E859312.40309@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <4E859312.40309@canonical.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Stefan Bader Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On Fri, Sep 30, 2011 at 11:59:46AM +0200, Stefan Bader wrote: > On 26.09.2011 21:34, Konrad Rzeszutek Wilk wrote: > > On Mon, Sep 26, 2011 at 09:22:21AM -0700, Jeremy Fitzhardinge wrote: > >> On 09/26/2011 06:13 AM, Konrad Rzeszutek Wilk wrote: > >>> which has git commit b8bcfe997e46150fedcc3f5b26b846400122fdd9. > >>> > >>> The unintended consequence of removing the flushing of MMU > >>> updates when doing kmap_atomic (or kunmap_atomic) is that we can > >>> hit a dereference bug when processing a "fork()" under a heavy loaded > >>> machine. Specifically we can hit: > >> > >> The patch is all OK, but I wouldn't have headlined it as a "partial > >> revert" - the important point is that the pte updates in k(un)map_atomic > >> need to be synchronous, regardless of whether we're in lazy_mmu mode. > >> > >> The fact that b8bcfe997e4 introduced the problem is interesting to note, > >> but only somewhat relevant to the analysis of what's being fixed here. > > > > Good point. How about > > > > Limiting the cc's for just asking about status... Ah, got this email: The patch titled Subject: x86/paravirt: PTE updates in k(un)map_atomic need to be synchronous, regardless of lazy_mmu mode has been added to the -mm tree. Its filename is x86-paravirt-pte-updates-in-kunmap_atomic-need-to-be-synchronous-regardless-of-lazy_mmu-mode.patch so it is definitly on the train.