Re: [Qemu-devel] [PULL 2/2] target/ppc: Fix setting of cpu->compat_pvr on incoming migration

[Greg Kurz]

On Mon, 27 Nov 2017 15:30:03 +1100
David Gibson <address@hidden> wrote:

> From: Suraj Jitindar Singh <address@hidden>
> 
> cpu->compat_pvr is used to store the current compat mode of the cpu.
> 
> On the receiving side during incoming migration we check compatibility
> with the compat mode by calling ppc_set_compat(). However we fail to set
> the compat mode with the hypervisor since the "new" compat mode doesn't
> differ from the current (due to a "cpu->compat_pvr != compat_pvr" check).
> This means that kvm runs the vcpus without a compat mode, which is the
> incorrect behaviour. The implication being that a compatibility mode
> will never be in effect after migration.
> 
> To fix this so that the compat mode is correctly set with the
> hypervisor, store the desired compat mode and reset cpu->compat_pvr to
> zero before calling ppc_set_compat().
> 
> Fixes: 5dfaa532 ("ppc: fix ppc_set_compat() with KVM PR")
> 

Cc'ing stable since 5dfaa532 was shipped with QEMU 2.10

> Signed-off-by: Suraj Jitindar Singh <address@hidden>
> Signed-off-by: David Gibson <address@hidden>
> ---
>  target/ppc/machine.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/target/ppc/machine.c b/target/ppc/machine.c
> index 384caee800..24117e8f31 100644
> --- a/target/ppc/machine.c
> +++ b/target/ppc/machine.c
> @@ -237,9 +237,11 @@ static int cpu_post_load(void *opaque, int version_id)
>  
>  #if defined(TARGET_PPC64)
>      if (cpu->compat_pvr) {
> +        uint32_t compat_pvr = cpu->compat_pvr;
>          Error *local_err = NULL;
>  
> -        ppc_set_compat(cpu, cpu->compat_pvr, &local_err);
> +        cpu->compat_pvr = 0;
> +        ppc_set_compat(cpu, compat_pvr, &local_err);
>          if (local_err) {
>              error_report_err(local_err);
>              return -1;