On Mon, 5 Dec 2016 15:09:16 +1100 David Gibson <da...@gibson.dropbear.id.au> wrote:
> On Fri, Dec 02, 2016 at 03:48:25PM +0100, Greg Kurz wrote:
> > On Wed, 16 Nov 2016 09:17:55 +1100
> > David Gibson <da...@gibson.dropbear.id.au> wrote:
> >
> > > Migrating between different CPU versions is quite complicated for ppc.
> > > A long time ago, we ensure identical CPU versions at either end by
> > > checking
> > > the PVR had the same value. However, this breaks under KVM HV, because
> > > we always have to use the host's PVR - it's not virtualized. That would
> > > mean we couldn't migrate between hosts with different PVRs, even if the
> > > CPUs are close enough to compatible in practice (sometimes identical cores
> > > with different surrounding logic have different PVRs, so this happens in
> > > practice quite often).
> > >
> > > So, we removed the PVR check, but instead checked that several flags
> > > indicating supported instructions matched. This turns out to be a bad
> > > idea, because those instruction masks are not architected information, but
> > > essentially a TCG implementation detail. So changes to qemu internal CPU
> > > modelling can break migration - this happened between qemu-2.6 and
> > > qemu-2.7.
> > >
> > > Modern server-class CPUs can be placed into compatibility modes. Now that
> > > we're handling those properly, we finally have the information to sanely
> > > deal with CPU compatibility across migration.
> > >
> > > This patch bumps the migration version number for the ppc CPU removing the
> > > instruction mask field (and some other unwise VMSTATE_EQUAL checks), and
> > > adding the compatibility PVR to the migration stream.
> > >
> >
> > Things have changed since you posted this RFC:
> >
> > commit 16a2497bd44cac1856e259654fd304079bd1dcdc
> > Author: David Gibson <da...@gibson.dropbear.id.au>
> > Date: Mon Nov 21 16:28:12 2016 +1100
> >
> > target-ppc: Fix CPU migration from qemu-2.6 <-> later versions
> >
> > and
> >
> > commit 146c11f16f12dbfea62cbd7f865614bb6fcbc6b5
> > Author: David Gibson <da...@gibson.dropbear.id.au>
> > Date: Mon Nov 21 16:29:30 2016 +1100
> >
> > target-ppc: Allow eventual removal of old migration mistakes
> >
> > I guess that the version bumping isn't necessary anymore if we keep these.
> >
> > I'll assume yes and rebase this patch against current master, simply
> > dropping
> > the version bumping and related lines.
>
> Yeah, I realised that breaking backwards migration was a bad idea, and
> with some help from Dave Gilbert worked out how to make it possible.
>
> I realize I'm going to have to rework my compat series in light of
> these changes.
>
While doing so, maybe you can fold the following in your patch, and thus
make tests/qom-test happy:
--- a/target-ppc/translate_init.c
+++ b/target-ppc/translate_init.c
@@ -32,6 +32,7 @@
#include "qapi/visitor.h"
#include "hw/qdev-properties.h"
#include "hw/ppc/ppc.h"
+#include "sysemu/qtest.h"
//#define PPC_DUMP_CPU
//#define PPC_DEBUG_SPR
@@ -8442,7 +8443,9 @@ POWERPC_FAMILY(POWER5P)(ObjectClass *oc, void *data)
static void getset_compat_deprecated(Object *obj, Visitor *v, const char *name,
void *opaque, Error **errp)
{
- error_report("CPU 'compat' property is deprecated and has no effect; use
max-cpu-compat machine property instead");
+ if (!qtest_enabled()) {
+ error_report("CPU 'compat' property is deprecated and has no effect;
use max-cpu-compat machine property instead");
+ }
visit_type_null(v, name, errp);
}
Also a friendly reminder: cpu registers get trashed during cpu post
load (see at the end of this mail).
Cheers.
--
Greg
> > > We consider the CPUs compatible for migration if:
> > > * The source was running in a compatibility mode which the destination
> > > supports
> > > OR * The source has a PVR matching the same qemu CPU class as the
> > > destination, either an exact match or an approximate match
> > > determined
> > > by the cpu class's pvr_match hook.
> > >
> > > Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
> > > ---
> > > target-ppc/machine.c | 87
> > > +++++++++++++++++++++++++++++++++++++++++++++++-----
> > > 1 file changed, 79 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/target-ppc/machine.c b/target-ppc/machine.c
> > > index e43cb6c..25a30d5 100644
> > > --- a/target-ppc/machine.c
> > > +++ b/target-ppc/machine.c
> > > @@ -8,6 +8,7 @@
> > > #include "helper_regs.h"
> > > #include "mmu-hash64.h"
> > > #include "migration/cpu.h"
> > > +#include "qapi/error.h"
> > >
> > > static int cpu_load_old(QEMUFile *f, void *opaque, int version_id)
> > > {
> > > @@ -163,6 +164,30 @@ static void cpu_pre_save(void *opaque)
> > > }
> > > }
> > >
> > > +/*
> > > + * Determine if a given PVR is a "close enough" match to the CPU
> > > + * object. For TCG and KVM PR it would probably be sufficient to
> > > + * require an exact PVR match. However for KVM HV the user is
> > > + * restricted to a PVR exactly matching the host CPU. The correct way
> > > + * to handle this is to put the guest into an architected
> > > + * compatibility mode. However, to allow a more forgiving transition
> > > + * and migration from before this was widely done, we allow migration
> > > + * between sufficiently similar PVRs, as determined by the CPU class's
> > > + * pvr_match() hook.
> > > + */
> > > +static bool pvr_match(PowerPCCPU *cpu, uint32_t pvr)
> > > +{
> > > + PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
> > > +
> > > + if (pvr == pcc->pvr) {
> > > + return true;
> > > + }
> > > + if (pcc->pvr_match) {
> > > + return pcc->pvr_match(pcc, pvr);
> > > + }
> > > + return false;
> > > +}
> > > +
> > > static int cpu_post_load(void *opaque, int version_id)
> > > {
> > > PowerPCCPU *cpu = opaque;
> > > @@ -171,10 +196,31 @@ static int cpu_post_load(void *opaque, int
> > > version_id)
> > > target_ulong msr;
> > >
> > > /*
> > > - * We always ignore the source PVR. The user or management
> > > - * software has to take care of running QEMU in a compatible mode.
> > > + * If we're operating in compat mode, we should be ok as long as
> > > + * the destination supports the same compatiblity mode.
> > > + *
> > > + * Otherwise, however, we require that the destination has exactly
> > > + * the same CPU model as the source.
> > > */
> > > - env->spr[SPR_PVR] = env->spr_cb[SPR_PVR].default_value;
> > > +
> > > +#if defined(TARGET_PPC64)
> > > + if (cpu->compat_pvr) {
> > > + Error *local_err = NULL;
> > > +
> > > + ppc_set_compat(cpu, cpu->compat_pvr, &local_err);
> >
> > This calls cpu_synchronize_state(CPU(cpu)) and trashes the registers. This
> > is the root cause behind the program interrupts I mentioned in another mail.
> >
> > Adding a sync_needed boolean argument to ppc_set_compat() seems to be enough
> > to get this working. So I'll just do that and rerun the tests.
> >
> > Cheers.
> >
>
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