On Mon, Nov 28, 2016 at 03:23:46PM +1100, David Gibson wrote: > On Sat, Nov 26, 2016 at 01:33:16AM +0100, Greg Kurz wrote: > > On Wed, 16 Nov 2016 09:17:43 +1100 > > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > > > This series is a significant rework to how we handle CPU compatibility > > > modes on ppc. > > > > > > * Information about compatibility modes was previously open coded and > > > scattered across a number of functions in both target-ppc and spapr > > > code. It's now brought together into a common table of > > > compatibility modes. > > > > > > * There was significant conceptual confusion about what a > > > compatibility mode means, and how it interacts with the machine > > > type. This cleans that up, clarifying that a compatibility mode > > > (as an externally set option) only makes sense on machine types > > > that don't permit the guest hypervisor privilege (i.e. 'pseries') > > > > > > * It was previously the user's (or management layer's) responsibility > > > to determine compatibility of CPUs on either end for migration. > > > This uses the compatibility modes to check that properly during an > > > incoming migration. > > > > > > * Some ill-considered sanity checks broke migration from 2.6 to 2.7, > > > due to some new instruction classes being added. This should avoid > > > a repeat of that problem for 2.8 (we may be able to backport a > > > minimal subset to 2.7-stable to fix the existing problem). > > > > > > Patches 1-3 are preliminary cleanups which could stand on their own. > > > Patches 4-12 are the compatibility mode cleanup proper. > > > > > > So far, this has been mimimally tested. There are quite a few > > > migration cases to check. For example: > > > > > > Basic: > > > > > > 1) Boot guest with -cpu host > > > Should go into POWER8 compat mode after CAS > > > Previously would have been raw mode > > > > > > Thanks for doing these detailed tests, Greg. > > > > > == QEMU == > > > > spapr_cas_pvr current=0, explicit_match=1, new=f000004 > > > > == guest == > > > > cpu : POWER8 (architected), altivec supported > > > > > 2) Boot guest with -machine pseries,max-cpu-compat=power7 -cpu host > > > Should go into POWER7 compat mode > > > > > > > == QEMU == > > > > spapr_cas_pvr current=f000003, explicit_match=1, new=f000003 > > > > == guest == > > > > cpu : POWER7 (architected), altivec supported > > > > > 3) Boot guest with -cpu host,compat=power7 > > > Should act as (2), but print a warning > > > > > > > With extra patch to add explicit null to string visitors: > > > > qapi: add explicit null to string input and output visitors > > Message-Id: <147954362297.28064.5118492606031513925.stgit@bahia> > > > > == QEMU == > > > > CPU 'compat' property is deprecated and has no effect; use max-cpu-compat > > machine > > property instead > > > > spapr_cas_pvr current=f000003, explicit_match=1, new=f000003 > > > > == guest == > > > > cpu : POWER7 (architected), altivec supported > > > > > 4) Boot guest via libvirt with power7 compat mode specified in XML > > > Should act as (3), (2) once we fix libvirt > > > > > > > Not tested yet. > > > > > 5) Hack guest to only advertise power7 compatibility, boot with -cpu host > > > Should go into POWER7 compat mode after CAS > > > > > > > == QEMU == > > > > spapr_cas_pvr current=0, explicit_match=1, new=f000003 > > > > == guest == > > > > cpu : POWER7 (architected), altivec supported > > > > > 6) Hack guest to only advertise real PVRs > > > Should remain in POWER8 raw mode after CAS > > > > > > > == QEMU == > > > > spapr_cas_pvr current=0, explicit_match=1, new=0 > > > > == guest == > > > > cpu : POWER8 (raw), altivec supported > > > > > 7) Hack guest to only advertise real PVRs > > > Boot with -machine pseries,max-cpu-compat=power8 > > > Should fail at CAS time > > > > > > > == QEMU == > > > > h_client_architecture_support() returns H_HARDWARE as > > expected because max-cpu-compat is set and no compat > > PVR was found (even though the real PVR was found). > > > > == guest == > > > > WARNING: ibm,client-architecture-support call FAILED! > > > > but the guest boots anyway and we end up with: > > > > cpu : POWER8 (architected), altivec supported > > > > This looks weird since the guest explicitly said it only > > supports real PVRs... raw mode like case 6) would make > > more sense IMHO but patch 11/12 sets the default to max-cpu-compat > > at machine reset time: > > > > + ppc_set_compat_all(spapr->max_compat_pvr, &error_abort); > > > > Maybe we should at least switch to raw mode, return an error > > and let the guest decide ? > > > > Another option would be to do as specified in LoPAPR section B.6.2.3 > > when no acceptable PVR was found and to simply terminate the guest. > > So.. I suspect this is probably good enough in practice, given that > all known guests will actually advertise compat modes. The FAILED > gives at least a hint as to what's going on. > > To get it strictly correct, then yes, I think terminating the guest is > probably the PAPRishly correct thing to do, although it's not clear > quite what we do then. We don't really have a mechanism for shutting > the VM down entirely (which might surprise management), and if we > reboot we're likely to just hit the same error again. > > Hence my inclination to only worry about those details if someone > starts hitting them for real.
Oh.. that said, I think we should at least throw in a meaningful error_report() since that should get propagated up to the error logs that mangement layers are likely to keep. > > > > 8) Hack guest to only advertise power7 compatibility, boot with -cpu host > > > Reboot to normal guest > > > Should go to power7 compat mode after CAS of boot 1 > > > Should revert to raw mode on reboot > > > SHould go to power8 compat mode after CAS of boot 2 > > > > > > > == QEMU == > > > > boot 1: spapr_cas_pvr current=0, explicit_match=1, new=f000003 > > boot 2: spapr_cas_pvr current=0, explicit_match=1, new=f000004 > > > > == guest == > > > > boot 1: cpu : POWER7 (architected), altivec supported > > boot 2: cpu : POWER8 (architected), altivec supported > > > > > Migration: > > > > > > > I'll give a try to migration next week. > > > > Cheers. > > > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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