Re: [Qemu-devel] [PATCHv2 1/5] target-ppc: Fix CPU migration from qemu-2.6 <-> later versions

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 21/11/16 16:31, David Gibson wrote:
> When migration for target-ppc was converted to vmstate, several
> VMSTATE_EQUAL() checks were foolishly included of things that really
> should be internal state.  Specifically we verified equality of the
> insns_flags and insns_flags2 fields, which are used within TCG to
> determine which groups of instructions are available on this cpu
> model.  Between qemu-2.6 and qemu-2.7 we made some changes to these
> classes which broke migration.
> 
> This path fixes migration both forwards and backwards.  On migration
> from 2.6 to later versions we import the fields into teporary
> variables, which we then ignore.  In migration backwards, we populate
> the temporary fields from the runtime fields, but mask out the bits
> which were added after qemu-2.6, allowing the VMSTATE_EQUAL in
> qemu-2.6 to accept the stream.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>


Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>

One question though - do we care about TCG migration at all? If so, we
could want to migrate these bits, just not with _EQUAL but rather check
that the source does not have bits which are not supported by the destination.



> ---
>  target-ppc/cpu.h     |  6 ++++++
>  target-ppc/machine.c | 29 +++++++++++++++++++++++++----
>  2 files changed, 31 insertions(+), 4 deletions(-)
> 
> diff --git a/target-ppc/cpu.h b/target-ppc/cpu.h
> index 1c90adb..7798b2e 100644
> --- a/target-ppc/cpu.h
> +++ b/target-ppc/cpu.h
> @@ -1166,6 +1166,12 @@ struct PowerPCCPU {
>      int cpu_dt_id;
>      uint32_t max_compat;
>      uint32_t cpu_version;
> +
> +    /* fields used only during migration for compatibility hacks */
> +    target_ulong mig_msr_mask;
> +    uint64_t mig_insns_flags;
> +    uint64_t mig_insns_flags2;
> +    uint32_t mig_nb_BATs;
>  };
>  
>  static inline PowerPCCPU *ppc_env_get_cpu(CPUPPCState *env)
> diff --git a/target-ppc/machine.c b/target-ppc/machine.c
> index e43cb6c..fcac263 100644
> --- a/target-ppc/machine.c
> +++ b/target-ppc/machine.c
> @@ -140,6 +140,21 @@ static void cpu_pre_save(void *opaque)
>      PowerPCCPU *cpu = opaque;
>      CPUPPCState *env = &cpu->env;
>      int i;
> +    uint64_t insns_compat_mask =
> +        PPC_INSNS_BASE | PPC_ISEL | PPC_STRING | PPC_MFTB
> +        | PPC_FLOAT | PPC_FLOAT_FSEL | PPC_FLOAT_FRES
> +        | PPC_FLOAT_FSQRT | PPC_FLOAT_FRSQRTE | PPC_FLOAT_FRSQRTES
> +        | PPC_FLOAT_STFIWX | PPC_FLOAT_EXT
> +        | PPC_CACHE | PPC_CACHE_ICBI | PPC_CACHE_DCBZ
> +        | PPC_MEM_SYNC | PPC_MEM_EIEIO | PPC_MEM_TLBIE | PPC_MEM_TLBSYNC
> +        | PPC_64B | PPC_64BX | PPC_ALTIVEC
> +        | PPC_SEGMENT_64B | PPC_SLBI | PPC_POPCNTB | PPC_POPCNTWD;
> +    uint64_t insns_compat_mask2 = PPC2_VSX | PPC2_VSX207 | PPC2_DFP | PPC2_DBRX
> +        | PPC2_PERM_ISA206 | PPC2_DIVE_ISA206
> +        | PPC2_ATOMIC_ISA206 | PPC2_FP_CVT_ISA206
> +        | PPC2_FP_TST_ISA206 | PPC2_BCTAR_ISA207
> +        | PPC2_LSQ_ISA207 | PPC2_ALTIVEC_207
> +        | PPC2_ISA205 | PPC2_ISA207S | PPC2_FP_CVT_S64 | PPC2_TM;
>  
>      env->spr[SPR_LR] = env->lr;
>      env->spr[SPR_CTR] = env->ctr;
> @@ -161,6 +176,12 @@ static void cpu_pre_save(void *opaque)
>          env->spr[SPR_IBAT4U + 2*i] = env->IBAT[0][i+4];
>          env->spr[SPR_IBAT4U + 2*i + 1] = env->IBAT[1][i+4];
>      }
> +
> +    /* Hacks for migration compatibility between 2.6, 2.7 & 2.8 */
> +    cpu->mig_msr_mask = env->msr_mask;
> +    cpu->mig_insns_flags = env->insns_flags & insns_compat_mask;
> +    cpu->mig_insns_flags2 = env->insns_flags2 & insns_compat_mask2;
> +    cpu->mig_nb_BATs = env->nb_BATs;
>  }
>  
>  static int cpu_post_load(void *opaque, int version_id)
> @@ -561,10 +582,10 @@ const VMStateDescription vmstate_ppc_cpu = {
>          /* FIXME: access_type? */
>  
>          /* Sanity checking */
> -        VMSTATE_UINTTL_EQUAL(env.msr_mask, PowerPCCPU),
> -        VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU),
> -        VMSTATE_UINT64_EQUAL(env.insns_flags2, PowerPCCPU),
> -        VMSTATE_UINT32_EQUAL(env.nb_BATs, PowerPCCPU),
> +        VMSTATE_UINTTL(mig_msr_mask, PowerPCCPU),
> +        VMSTATE_UINT64(mig_insns_flags, PowerPCCPU),
> +        VMSTATE_UINT64(mig_insns_flags2, PowerPCCPU),
> +        VMSTATE_UINT32(mig_nb_BATs, PowerPCCPU),
>          VMSTATE_END_OF_LIST()
>      },
>      .subsections = (const VMStateDescription*[]) {
> 


-- 
Alexey