Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932953AbaJVKcU (ORCPT ); Wed, 22 Oct 2014 06:32:20 -0400 Received: from e06smtp10.uk.ibm.com ([195.75.94.106]:36357 "EHLO e06smtp10.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932715AbaJVKcS (ORCPT ); Wed, 22 Oct 2014 06:32:18 -0400 Date: Wed, 22 Oct 2014 12:32:08 +0200 From: Dominik Dingel To: Paolo Bonzini Cc: Andrew Morton , linux-mm@kvack.org, Mel Gorman , Michal Hocko , Dave Hansen , Rik van Riel , Andrea Arcangeli , Andy Lutomirski , "Aneesh Kumar K.V" , Bob Liu , Christian Borntraeger , Cornelia Huck , Gleb Natapov , Heiko Carstens , "H. Peter Anvin" , Hugh Dickins , Ingo Molnar , Jianyu Zhan , Johannes Weiner , "Kirill A. Shutemov" , kvm@vger.kernel.org, linux390@de.ibm.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Martin Schwidefsky Subject: Re: [PATCH 3/4] s390/mm: prevent and break zero page mappings in case of storage keys Message-ID: <20141022123208.3bcb6cfb@BR9TG4T3.de.ibm.com> In-Reply-To: <5447825B.5040608@redhat.com> References: <1413966624-12447-1-git-send-email-dingel@linux.vnet.ibm.com> <1413966624-12447-4-git-send-email-dingel@linux.vnet.ibm.com> <5447825B.5040608@redhat.com> Organization: IBM X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14102210-0041-0000-0000-000001C500A4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 22 Oct 2014 12:09:31 +0200 Paolo Bonzini wrote: > On 10/22/2014 10:30 AM, Dominik Dingel wrote: > > As use_skey is already the condition on which we call s390_enable_skey > > we need to introduce a new flag for the mm->context on which we decide > > if zero page mapping is allowed. > > Can you explain better why "mm->context.use_skey = 1" cannot be done > before the walk_page_range? Where does the walk or __s390_enable_skey > or (after the next patch) ksm_madvise rely on > "mm->context.forbids_zeropage && !mm->context.use_skey"? I can't, my reasoning there is wrong. I remembered incorrectly that we use mm_use_skey in arch/s390/kvm/priv.c to check if we need to call s390_enable_skey, but that does happen with the interception bits. So every vCPU which get the a interception for a storage key instruction will call s390_enable_skey and wait there for the mmap_sem. > The only reason I can think of, is that the next patch does not reset > "mm->context.forbids_zeropage" to 0 if the ksm_madvise fails. Why > doesn't it do that---or is it a bug? You are right, this is a bug, where we will drop to userspace with -ENOMEM. I will fix this as well. > Thanks, and sorry for the flurry of questions! :) I really appreciate your questions and remarks. Thank you! > Paolo > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/