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Re: [Qemu-ppc] [PATCH for-2.13 02/10] spapr: Remove support for PowerPC

From: Thomas Huth
Subject: Re: [Qemu-ppc] [PATCH for-2.13 02/10] spapr: Remove support for PowerPC 970 with pseries machine type
Date: Fri, 20 Apr 2018 07:58:36 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0

On 19.04.2018 19:21, Greg Kurz wrote:
> On Tue, 17 Apr 2018 17:17:14 +1000
> David Gibson <address@hidden> 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.


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