From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id 9BEEF6B0006 for ; Mon, 25 Jun 2018 03:57:21 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id r8-v6so4672886pgq.2 for ; Mon, 25 Jun 2018 00:57:21 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id h26-v6si13733693pfd.253.2018.06.25.00.57.19 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 25 Jun 2018 00:57:20 -0700 (PDT) Date: Mon, 25 Jun 2018 09:57:15 +0200 From: Michal Hocko 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: Sender: owner-linux-mm@kvack.org List-ID: 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 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