Re: [Xen-devel] [PATCH V3] xen: Fix BUFIOREQ evtchn init for a stubdom.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.07.12 at 17:41, Anthony PERARD <anthony.perard@xxxxxxxxxx> wrote:
> This is a missing part from the previous patch that add the BUFIOREQ_EVTCHN
> parameter. This patch changes the ownership of the buifioreq event channel 
> to
> the stubdom (when HVM_PARAM_DM_DOMAIN is set within the stubdom).
> 
> This patch introduces an helper to replace a xen port.
> 
> This fix the initialization of QEMU inside the stubdomain.
> 
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> ---
> Change v3:
>   For the bufioreq replacement:
>   - the code is now out of the vcpu loop
>   - the code does not take a lock anymore
>   - rename int *port to int *p_port
> Change v2:
>   - an helper
>   - the replacement of the buferioreq evtchn is inside iorp->lock now.
> 
>  xen/arch/x86/hvm/hvm.c |   32 ++++++++++++++++++++++----------
>  1 files changed, 22 insertions(+), 10 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index e0d495d..c2dfa73 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -3664,6 +3664,21 @@ static int hvmop_flush_tlb_all(void)
>      return 0;
>  }
>  
> +static int hvm_replace_event_channel(struct vcpu *v, uint64_t remote_domid,
> +                                     int *p_port)
> +{
> +    int old_port, new_port;
> +
> +    new_port = alloc_unbound_xen_event_channel(v, remote_domid, NULL);
> +    if ( new_port < 0 )
> +        return new_port;
> +
> +    /* xchg() ensures that only we free_xen_event_channel() */
> +    old_port = xchg(p_port, new_port);
> +    free_xen_event_channel(v, old_port);
> +    return 0;
> +}
> +
>  long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE(void) arg)
>  
>  {
> @@ -3775,19 +3790,16 @@ long do_hvm_op(unsigned long op, 
> XEN_GUEST_HANDLE(void) arg)
>                  rc = 0;
>                  domain_pause(d); /* safe to change per-vcpu xen_port */
>                  iorp = &d->arch.hvm_domain.ioreq;
> +                if (d->vcpu[0])
> +                    hvm_replace_event_channel(d->vcpu[0], a.value,
> +                        
> (int*)&d->vcpu[0]->domain->arch.hvm_domain.params[HVM_PARAM_BUFIOREQ_EVTCHN]);

Did I overlook this in v2? You clearly need to handle the error
case here (it is being handled, albeit - but that's not your patch's
fault - only in a rudimentary way, inside the loop).

Jan

>                  for_each_vcpu ( d, v )
>                  {
> -                    int old_port, new_port;
> -                    new_port = alloc_unbound_xen_event_channel(
> -                        v, a.value, NULL);
> -                    if ( new_port < 0 )
> -                    {
> -                        rc = new_port;
> +                    rc = hvm_replace_event_channel(v, a.value,
> +                                                   
> &v->arch.hvm_vcpu.xen_port);
> +                    if ( rc )
>                          break;
> -                    }
> -                    /* xchg() ensures that only we free_xen_event_channel() 
> */
> -                    old_port = xchg(&v->arch.hvm_vcpu.xen_port, new_port);
> -                    free_xen_event_channel(v, old_port);
> +
>                      spin_lock(&iorp->lock);
>                      if ( iorp->va != NULL )
>                          get_ioreq(v)->vp_eport = v->arch.hvm_vcpu.xen_port;
> -- 
> Anthony PERARD




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