From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 1/4] kvm-s390: add capability indicating COW support Date: Tue, 15 May 2012 15:24:49 +0300 Message-ID: <4FB24B11.1050607@redhat.com> References: <1337084128-38219-1-git-send-email-borntraeger@de.ibm.com> <1337084128-38219-2-git-send-email-borntraeger@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Marcelo Tossati , Carsten Otte , Alexander Graf , Jens Freimann , Cornelia Huck , Heiko Carstens , Martin Schwidefsky , Heinz Graalfs , KVM To: Christian Borntraeger Return-path: Received: from mx1.redhat.com ([209.132.183.28]:36802 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757589Ab2EOMZE (ORCPT ); Tue, 15 May 2012 08:25:04 -0400 In-Reply-To: <1337084128-38219-2-git-send-email-borntraeger@de.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: On 05/15/2012 03:15 PM, Christian Borntraeger wrote: > Currently qemu/kvm on s390 uses a guest mapping that does not > allow the guest backing page table to be write-protected to > support older systems. On those older systems a host write > protection fault will be delivered to the guest. > > 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? Or is qemu just passing the capability on to the guest? 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. -- error compiling committee.c: too many arguments to function