Re: [Qemu-devel] [PATCH] target-ppc: Remove PVR check from migration

[Alexander Graf]

On 15.04.14 07:06, Alexey Kardashevskiy wrote:
> Currently migration fails if CPU version (PVR register) is different
> even a bit. This check is performed at the very end of migration when
> device states are sent. This is too late for management software and
> we need to provide a way for the user to make sure that migration
> will succeed if QEMU is started with appropritate command line parameters.
>
> This removes the PVR check.
>
> This resets PVR to the default value as the existing VMSTATE record
> for SPR array sends all 1024 registers unconditionally and overwrites
> the destination PVR.
>
> If the user wants some guarantees for migration to succeed, then
> a CPU name or "host" CPU with a "compat" option (on its way to upsteam)
> should be used and KVM or TCG is expected to fail on unsupported values
> at the moment of QEMU start.
>
> Cc: Bharata B Rao <address@hidden>
> Signed-off-by: Alexey Kardashevskiy <address@hidden>
> ---
>
>
> We should propably reset to the default value all SPRs which do not have
> env->spr_cb[num]->oea_write callback initialized. Yes, in a separate patch.
> What can it possibly break?

oea_write means that supervisor state can change the state. What about 
registers like LPCR which are hypervisor privileged? Those wouldn't have 
a callback, but still change thanks to H_SET_MODE, no?

Thanks, applied to ppc-next.


Alex

> ---
>   target-ppc/machine.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/target-ppc/machine.c b/target-ppc/machine.c
> index 063b379..df7cfc5 100644
> --- a/target-ppc/machine.c
> +++ b/target-ppc/machine.c
> @@ -160,6 +160,11 @@ static int cpu_post_load(void *opaque, int version_id)
>       CPUPPCState *env = &cpu->env;
>       int i;
>   
> +    /*
> +     * We always ignore the source PVR. The user or management
> +     * software has to take care of running QEMU in a compatible mode.
> +     */
> +    env->spr[SPR_PVR] = env->spr_cb[SPR_PVR].default_value;
>       env->lr = env->spr[SPR_LR];
>       env->ctr = env->spr[SPR_CTR];
>       env->xer = env->spr[SPR_XER];
> @@ -471,8 +476,7 @@ const VMStateDescription vmstate_ppc_cpu = {
>       .pre_save = cpu_pre_save,
>       .post_load = cpu_post_load,
>       .fields      = (VMStateField []) {
> -        /* Verify we haven't changed the pvr */
> -        VMSTATE_UINTTL_EQUAL(env.spr[SPR_PVR], PowerPCCPU),
> +        VMSTATE_UNUSED(sizeof(target_ulong)), /* was _EQUAL(env.spr[SPR_PVR]) 
> */
>   
>           /* User mode architected state */
>           VMSTATE_UINTTL_ARRAY(env.gpr, PowerPCCPU, 32),