Re: [Qemu-devel] [RFC 12/17] ppc: Migrate compatibility mode

[Alexey Kardashevskiy]

On 30/10/16 22:12, David Gibson wrote:
> Server-class POWER CPUs can be put into several compatibility modes.  These
> can be specified on the command line, or negotiated by the guest during
> boot.
> 
> Currently we don't migrate the compatibility mode, which means after a
> migration the guest will revert to running with whatever compatibility
> mode (or none) specified on the command line.
> 
> With the limited range of CPUs currently used, this doesn't usually cause
> a problem, but it could.  Fix this by adding the compatibility mode (if
> set) to the migration stream.
> 
> Signed-off-by: David Gibson <address@hidden>
> ---
>  target-ppc/machine.c | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/target-ppc/machine.c b/target-ppc/machine.c
> index 4820f22..5d87ff6 100644
> --- a/target-ppc/machine.c
> +++ b/target-ppc/machine.c
> @@ -9,6 +9,7 @@
>  #include "mmu-hash64.h"
>  #include "migration/cpu.h"
>  #include "exec/exec-all.h"
> +#include "qapi/error.h"
>  
>  static int cpu_load_old(QEMUFile *f, void *opaque, int version_id)
>  {
> @@ -176,6 +177,20 @@ static int cpu_post_load(void *opaque, int version_id)
>       * software has to take care of running QEMU in a compatible mode.
>       */
>      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;
> +        }
> +    }
> +#endif
> +
>      env->lr = env->spr[SPR_LR];
>      env->ctr = env->spr[SPR_CTR];
>      cpu_write_xer(env, env->spr[SPR_XER]);
> @@ -528,6 +543,24 @@ static const VMStateDescription vmstate_tlbmas = {
>      }
>  };
>  
> +static bool compat_needed(void *opaque)
> +{
> +    PowerPCCPU *cpu = opaque;
> +
> +    return cpu->compat_pvr != 0;


Finally got to trying how this affects migration :)

This breaks migration to QEMU <=2.7, and it should not at least when both
source and destination are running with  -cpu host,compat=power7.


> +}
> +
> +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,
> @@ -580,6 +613,7 @@ const VMStateDescription vmstate_ppc_cpu = {
>          &vmstate_tlb6xx,
>          &vmstate_tlbemb,
>          &vmstate_tlbmas,
> +        &vmstate_compat,
>          NULL
>      }
>  };
> 


-- 
Alexey