From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38839) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f9P4P-0005AV-G9 for qemu-devel@nongnu.org; Fri, 20 Apr 2018 01:58:54 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f9P4L-0000ZN-9Y for qemu-devel@nongnu.org; Fri, 20 Apr 2018 01:58:53 -0400 References: <20180417071722.9399-1-david@gibson.dropbear.id.au> <20180417071722.9399-3-david@gibson.dropbear.id.au> <20180419192105.7eb51b26@bahia.lan> From: Thomas Huth Message-ID: Date: Fri, 20 Apr 2018 07:58:36 +0200 MIME-Version: 1.0 In-Reply-To: <20180419192105.7eb51b26@bahia.lan> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH for-2.13 02/10] spapr: Remove support for PowerPC 970 with pseries machine type List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Greg Kurz , David Gibson Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org On 19.04.2018 19:21, Greg Kurz wrote: > On Tue, 17 Apr 2018 17:17:14 +1000 > David Gibson wrote: > >> Current POWER cpus allow for a VRMA, a special mapping which describes a >> guest's view of memory when in real mode (MMU off, from the guest's point >> of view). Older cpus didn't have that which meant that to support a guest >> a special host-contiguous region of memory was needed to give the guest its >> Real Mode Area (RMA). >> >> This was useful in the early days of KVM on Power to allow it to be tested >> on PowerPC 970 chips as used in Macintosh G5 machines. Now, however, those >> machines are so old as to be irrelevant, and the host kernel has long since >> dropped support for this mode. It hasn't been tested in ages either. >> >> So, to simplify the code, drop the support from qemu as well. >> > > So this could possibly break TCG guests with 970, which happens to be > bootable with the current code ? > > $ cat /etc/redhat-release > Red Hat Enterprise Linux Server release 6.9 (Santiago) > $ cat /proc/cpuinfo > processor : 0 > cpu : PPC970, altivec supported > clock : 1000.000000MHz > revision : 2.2 (pvr 0039 0202) > > timebase : 512000000 > platform : pSeries > model : IBM pSeries (emulated by qemu) > machine : CHRP IBM pSeries (emulated by qemu) > > I guess nobody uses this setup, but my understanding is that some > rules must be followed when it comes to removing something that > works. > > https://wiki.qemu.org/Features/LegacyRemoval#Rules_for_removing_an_interface > > Maybe add a warning if 970 is used, and turn it into an error in two releases > along with this patch ? Right, we've got a process for deprecating old features, so please follow that process. Thomas