On 19.04.2018 19:21, Greg Kurz wrote: > On Tue, 17 Apr 2018 17:17:14 +1000 > David Gibson <da...@gibson.dropbear.id.au> 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
