Re: [Qemu-devel] [PATCH 02/10] apic_common: vapic_paddr synchronization fix

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Sep 09, 2014 at 02:30:01PM +0200, Paolo Bonzini wrote:
> From: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
> 
> This patch postpones vapic_paddr initialization, which is performed
> during migration. When vapic_paddr is synchronized within the migration
> process, apic_common functions could operate with incorrect apic state,
> if it hadn't loaded yet. This patch postpones the synchronization until
> the virtual machine is started, ensuring that the whole virtual machine
> state has been loaded.
> 
> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  hw/i386/kvmvapic.c | 37 ++++++++++++++++++++++++++-----------
>  1 file changed, 26 insertions(+), 11 deletions(-)
> 
> diff --git a/hw/i386/kvmvapic.c b/hw/i386/kvmvapic.c
> index ee95963..2bcc249 100644
> --- a/hw/i386/kvmvapic.c
> +++ b/hw/i386/kvmvapic.c
> @@ -59,6 +59,7 @@ typedef struct VAPICROMState {
>      GuestROMState rom_state;
>      size_t rom_size;
>      bool rom_mapped_writable;
> +    VMChangeStateEntry *vmsentry;
>  } VAPICROMState;
>  
>  #define TYPE_VAPIC "kvmvapic"
> @@ -734,11 +735,34 @@ static void do_vapic_enable(void *data)
>      vapic_enable(s, cpu);
>  }
>  
> -static int vapic_post_load(void *opaque, int version_id)
> +static void kvmvapic_vm_state_change(void *opaque, int running,
> +				     RunState state)
>  {
>      VAPICROMState *s = opaque;
>      uint8_t *zero;
>  
> +    if (!running) {
> +        return;
> +    }
> +
> +    if (s->state == VAPIC_ACTIVE) {
> +        if (smp_cpus == 1) {

maybe add a comment explaining why we need
to special case smp_cpus?

> +            run_on_cpu(first_cpu, do_vapic_enable, s);

Is this safe to do in vmstate handler? cpu isn't running yet is it?

> +        } else {
> +            zero = g_malloc0(s->rom_state.vapic_size);
> +            cpu_physical_memory_write(s->vapic_paddr, zero,
> +                                      s->rom_state.vapic_size);
> +            g_free(zero);
> +        }
> +    }
> +
> +    qemu_del_vm_change_state_handler(s->vmsentry);
> +}
> +
> +static int vapic_post_load(void *opaque, int version_id)
> +{
> +    VAPICROMState *s = opaque;
> +
>      /*
>       * The old implementation of qemu-kvm did not provide the state
>       * VAPIC_STANDBY. Reconstruct it.
> @@ -752,17 +776,8 @@ static int vapic_post_load(void *opaque, int version_id)
>              return -1;
>          }
>      }
> -    if (s->state == VAPIC_ACTIVE) {
> -        if (smp_cpus == 1) {
> -            run_on_cpu(first_cpu, do_vapic_enable, s);
> -        } else {
> -            zero = g_malloc0(s->rom_state.vapic_size);
> -            cpu_physical_memory_write(s->vapic_paddr, zero,
> -                                      s->rom_state.vapic_size);
> -            g_free(zero);
> -        }
> -    }
>  
> +    s->vmsentry = qemu_add_vm_change_state_handler(kvmvapic_vm_state_change, s);
>      return 0;
>  }
>  
> -- 
> 2.1.0
> 
>