From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:48667) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UgiB3-0006lq-4E for qemu-devel@nongnu.org; Sun, 26 May 2013 17:08:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UgiAx-0002UJ-QJ for qemu-devel@nongnu.org; Sun, 26 May 2013 17:08:29 -0400 Received: from e06smtp15.uk.ibm.com ([195.75.94.111]:45987) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UgiAx-0002TN-G4 for qemu-devel@nongnu.org; Sun, 26 May 2013 17:08:23 -0400 Received: from /spool/local by e06smtp15.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sun, 26 May 2013 22:04:29 +0100 Received: from b06cxnps3075.portsmouth.uk.ibm.com (d06relay10.portsmouth.uk.ibm.com [9.149.109.195]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id 1754D1B0805F for ; Sun, 26 May 2013 22:08:18 +0100 (BST) Received: from d06av11.portsmouth.uk.ibm.com (d06av11.portsmouth.uk.ibm.com [9.149.37.252]) by b06cxnps3075.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r4QL87on54788310 for ; Sun, 26 May 2013 21:08:07 GMT Received: from d06av11.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av11.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r4QL8H3a017994 for ; Sun, 26 May 2013 15:08:17 -0600 Message-ID: <51A279C0.50601@de.ibm.com> Date: Sun, 26 May 2013 23:08:16 +0200 From: Christian Borntraeger MIME-Version: 1.0 References: <1369414987-8839-1-git-send-email-pbonzini@redhat.com> <1369414987-8839-13-git-send-email-pbonzini@redhat.com> <51A218DF.2070506@suse.de> <51A25D60.9000502@redhat.com> In-Reply-To: <51A25D60.9000502@redhat.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH 12/15] s390x: reduce TARGET_PHYS_ADDR_SPACE_BITS to 62 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Alexander Graf , =?ISO-8859-15?Q?Andreas_F=E4rber?= , Avi Kivity , qemu-devel@nongnu.org On 26/05/13 21:07, Paolo Bonzini wrote: > Il 26/05/2013 16:14, Andreas Färber ha scritto: >>> With the next patch, the memory API will complain if the >>> TARGET_PHYS_ADDR_SPACE_BITS gets dangerously close to an >>> overflow. s390x can handle up to 64 bit of physical address >>> space from its page tables, but we never use that much. Just >>> decrease the value. >>> >>> Cc: Alexander Graf >>> Signed-off-by: Paolo Bonzini >> >> Didn't Avi introduce 128-bit arithmetic into QEMU to avoid 64-bit values >> overflowing? Why are you limiting Memory API to 62-bit now? > > The next patch makes a difference between artificial memory regions > (containers and aliases) which can have arbitrary placement and width, > and the final view of the address space which cannot have a full 64-bit > size. > > 63 bits probably would work, but I preferred to be safe since 62 is the > largest used by other targets. > > It should be fixable, but if it is not a problem I wouldn't worry much > about it. I would prefer to allow 64bit of address space. Memory on s390x can be discontiguous. It is currently not used under KVM and it might not make a lot of sense, but the current KVM code would allow a guest that has a layout of lets say 0...1GB + 16EB-1GB...16EB. Furthermore, I know of some (prototype only) hw memory devices that actually populated the upper memory addresses. If such a thing becomes reality in the future we cannot provide virtualization of those. Christian