From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EF1FAC43142 for ; Mon, 25 Jun 2018 07:57:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A1C5425117 for ; Mon, 25 Jun 2018 07:57:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A1C5425117 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752214AbeFYH5U (ORCPT ); Mon, 25 Jun 2018 03:57:20 -0400 Received: from mx2.suse.de ([195.135.220.15]:51287 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752402AbeFYH5S (ORCPT ); Mon, 25 Jun 2018 03:57:18 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (charybdis-ext-too.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 3179DAB09; Mon, 25 Jun 2018 07:57:17 +0000 (UTC) Date: Mon, 25 Jun 2018 09:57:15 +0200 From: Michal Hocko To: Paolo Bonzini Cc: LKML , kvm@vger.kernel.org, Radim =?utf-8?B?S3LEjW3DocWZ?= , linux-mm@kvack.org, Andrea Arcangeli , =?iso-8859-1?B?Suly9G1l?= Glisse Subject: Re: [RFC PATCH] mm, oom: distinguish blockable mode for mmu notifiers Message-ID: <20180625075715.GA28965@dhcp22.suse.cz> References: <20180622150242.16558-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun 24-06-18 10:11:21, Paolo Bonzini wrote: > On 22/06/2018 17:02, Michal Hocko wrote: > > @@ -7215,6 +7216,8 @@ void kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm, > > apic_address = gfn_to_hva(kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT); > > if (start <= apic_address && apic_address < end) > > kvm_make_all_cpus_request(kvm, KVM_REQ_APIC_PAGE_RELOAD); > > + > > + return 0; > > This is wrong, gfn_to_hva can sleep. Hmm, I have tried to crawl the call chain and haven't found any sleepable locks taken. Maybe I am just missing something. __kvm_memslots has a complex locking assert. I do not see we would take slots_lock anywhere from the notifier call path. IIUC that means that users_count has to be zero at that time. I have no idea how that is guaranteed. > You could do the the kvm_make_all_cpus_request unconditionally, but only > if !blockable is a really rare thing. OOM would be fine, since the > request actually would never be processed, but I'm afraid of more uses > of !blockable being introduced later. Well, if this is not generally guaranteed then I have to come up with a different flag. E.g. OOM_CONTEXT that would be more specific to contrains for the callback. -- Michal Hocko SUSE Labs