From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757797Ab3B0WlY (ORCPT ); Wed, 27 Feb 2013 17:41:24 -0500 Received: from terminus.zytor.com ([198.137.202.10]:58610 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751592Ab3B0WlW (ORCPT ); Wed, 27 Feb 2013 17:41:22 -0500 Message-ID: <512E8B41.8000504@zytor.com> Date: Wed, 27 Feb 2013 14:40:01 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130219 Thunderbird/17.0.3 MIME-Version: 1.0 To: Greg KH CC: Boris Ostrovsky , mingo@redhat.com, konrad.wilk@oracle.com, tglx@linutronix.de, xen-devel@lists.xen.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/x86: Flush lazy MMU when DEBUG_PAGEALLOC is set References: <91983d94-7b7d-4a0b-9470-e7cd823ba139@default> In-Reply-To: <91983d94-7b7d-4a0b-9470-e7cd823ba139@default> X-Enigmail-Version: 1.5 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Greg, policy opinion? -hpa On 02/26/2013 03:57 PM, Boris Ostrovsky wrote: > > ----- hpa@zytor.com wrote: > >> On 02/26/2013 02:56 PM, Boris Ostrovsky wrote: >>> When CONFIG_DEBUG_PAGEALLOC is set page table updates made by >>> kernel_map_pages() are not made visible (via TLB flush) immediately >> if lazy >>> MMU is on. In environments that support lazy MMU (e.g. Xen) this may >> lead to >>> fatal page faults, for example, when zap_pte_range() needs to >> allocate pages >>> in __tlb_remove_page() -> tlb_next_batch(). >>> >>> Signed-off-by: Boris Ostrovsky >>> --- >>> arch/x86/mm/pageattr.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>> >>> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c >>> index ca1f1c2..7b3216e 100644 >>> --- a/arch/x86/mm/pageattr.c >>> +++ b/arch/x86/mm/pageattr.c >>> @@ -1369,6 +1369,8 @@ void kernel_map_pages(struct page *page, int >> numpages, int enable) >>> * but that can deadlock->flush only current cpu: >>> */ >>> __flush_tlb_all(); >>> + >>> + arch_flush_lazy_mmu_mode(); >>> } >>> >>> #ifdef CONFIG_HIBERNATION >>> >> >> This sounds like a critical fix, i.e. a -stable candidate. Am I >> correct? > > I considered copying stable but then I decided that this is a debugging feature > --- kernel_map_pages() is only defined if CONFIG_DEBUG_PAGEALLOC is set and my > thinking was that stable kernels usually don't do this. > > > -boris >