From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39574) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dGJW2-0003tE-68 for qemu-devel@nongnu.org; Thu, 01 Jun 2017 02:23:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dGJVy-0006q5-5e for qemu-devel@nongnu.org; Thu, 01 Jun 2017 02:23:26 -0400 Message-ID: <1496298190.4414.2.camel@gmail.com> From: Suraj Jitindar Singh Date: Thu, 01 Jun 2017 16:23:10 +1000 In-Reply-To: <20170526052319.28096-6-david@gibson.dropbear.id.au> References: <20170526052319.28096-1-david@gibson.dropbear.id.au> <20170526052319.28096-6-david@gibson.dropbear.id.au> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCHv4 5/5] ppc: Rework CPU compatibility testing across migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson , groug@kaod.org, clg@kaod.org, aik@ozlabs.ru, mdroth@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com Cc: quintela@redhat.com, sursingh@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, qemu-ppc@nongnu.org, abologna@redhat.com, sbobroff@redhat.com, dgilbert@redhat.com On Fri, 2017-05-26 at 15:23 +1000, David Gibson wrote: > Migrating between different CPU versions is a bit complicated for > ppc. > A long time ago, we ensured 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.  That was addressed by 146c11f1 "target-ppc: Allow eventual > removal of old migration mistakes". > > Now, verification of CPU compatibility across a migration basically > doesn't > happen.  We simply ignore the PVR of the incoming migration, and hope > the > cpu on the destination is close enough to work. > > Now that we've cleaned up handling of processor compatibility modes > for > pseries machine type, we can do better.  We allow migration if: > >     * The source and destination PVRs are for the same type of CPU, > as >       determined by CPU class's pvr_match function > OR  * When the source was in a compatibility mode, and the > destination CPU >       supports the same compatibility mode > > Signed-off-by: David Gibson Looks good to me. Reviewed-by: Suraj Jitindar Singh > --- >  target/ppc/machine.c | 72 > +++++++++++++++++++++++++++++++++++++++++++++++++--- >  1 file changed, 69 insertions(+), 3 deletions(-) > > diff --git a/target/ppc/machine.c b/target/ppc/machine.c > index 6cb3a48..2c6d9dc 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) >  { > @@ -195,6 +196,30 @@ 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; > @@ -203,10 +228,31 @@ 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); > +        if (local_err) { > +            error_report_err(local_err); > +            error_free(local_err); > +            return -1; > +        } > +    } else > +#endif > +    { > +        if (!pvr_match(cpu, env->spr[SPR_PVR])) { > +            return -1; > +        } > +    } > + >      env->lr = env->spr[SPR_LR]; >      env->ctr = env->spr[SPR_CTR]; >      cpu_write_xer(env, env->spr[SPR_XER]); > @@ -560,6 +606,25 @@ static const VMStateDescription vmstate_tlbmas = > { >      } >  }; >   > +static bool compat_needed(void *opaque) > +{ > +    PowerPCCPU *cpu = opaque; > + > +    assert(!(cpu->compat_pvr && !cpu->vhyp)); > +    return (cpu->compat_pvr != 0); > +} > + > +static const VMStateDescription vmstate_compat = { > +    .name = "cpu/compat", > +    .version_id = 1, > +    .minimum_version_id = 1, > +    .needed = compat_needed, > +    .fields = (VMStateField[]) { > +        VMSTATE_UINT32(compat_pvr, PowerPCCPU), > +        VMSTATE_END_OF_LIST() > +    } > +}; > + >  const VMStateDescription vmstate_ppc_cpu = { >      .name = "cpu", >      .version_id = 5, > @@ -613,6 +678,7 @@ const VMStateDescription vmstate_ppc_cpu = { >          &vmstate_tlb6xx, >          &vmstate_tlbemb, >          &vmstate_tlbmas, > +        &vmstate_compat, >          NULL >      } >  };