From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Borntraeger <borntraeger@de.ibm.com>
Subject: Re: [PATCH 1/4] kvm-s390: add capability indicating COW support
Date: Tue, 15 May 2012 14:31:49 +0200
Message-ID: <4FB24CB5.3070606@de.ibm.com>
References: <1337084128-38219-1-git-send-email-borntraeger@de.ibm.com> <1337084128-38219-2-git-send-email-borntraeger@de.ibm.com> <4FB24B11.1050607@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Cc: Marcelo Tossati <mtosatti@redhat.com>,
	Carsten Otte <cotte@de.ibm.com>,
	Alexander Graf <agraf@suse.de>,
	Jens Freimann <jfrei@linux.vnet.ibm.com>,
	Cornelia Huck <cornelia.huck@de.ibm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Heinz Graalfs <graalfs@linux.vnet.ibm.com>,
	KVM <kvm@vger.kernel.org>
To: Avi Kivity <avi@redhat.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:49605 "EHLO
	e06smtp12.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1758759Ab2EOMcV (ORCPT <rfc822;kvm@vger.kernel.org>);
	Tue, 15 May 2012 08:32:21 -0400
Received: from /spool/local
	by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted
	for <kvm@vger.kernel.org> from <borntraeger@de.ibm.com>;
	Tue, 15 May 2012 13:32:19 +0100
Received: from d06av02.portsmouth.uk.ibm.com (d06av02.portsmouth.uk.ibm.com [9.149.37.228])
	by d06nrmr1707.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q4FCVm4B2269354
	for <kvm@vger.kernel.org>; Tue, 15 May 2012 13:31:48 +0100
Received: from d06av02.portsmouth.uk.ibm.com (loopback [127.0.0.1])
	by d06av02.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q4FCVlTa023725
	for <kvm@vger.kernel.org>; Tue, 15 May 2012 06:31:48 -0600
In-Reply-To: <4FB24B11.1050607@redhat.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On 15/05/12 14:24, Avi Kivity wrote:
>> Newer systems allow to write-protect the guest backing memory
>> and let the fault be delivered to the host, thus allowing COW.
>>
>> Use a capability bit to tell qemu if that is possible.
>>
> 
> Asking out of ignorance: who is doing the write protection here? The
> guest?  If so, why is qemu involved?

It is about the host doing write protection of guest/user memory (e.g. for 
dirty pages tracking or KSM)

> btw, we usually use 'userspace' in kernel patches instead of qemu to
> create the illusion that it's not the only consumer of kvm interfaces.

In fact there are other consumers.