Re: [Xen-devel] [PATCH RFC 1/4] xen: evtchn: make evtchn_reset() ready for soft reset

[Tim Deegan <tim@xxxxxxx>]

At 15:35 +0200 on 03 Jun (1433345719), Vitaly Kuznetsov wrote:
> We need to close all event channel so the domain performing soft reset
> will be able to open them back. Interdomain channels are, however,
> special. We need to keep track of who opened it as in (the most common)
> case it was opened by the control domain we won't be able (and allowed) to
> re-establish it.


I'm not sure I understand -- can you give an example of what this is
avoiding?  I would have thought that the kexec'ing VM needs to tear
down _all_ its connections and then restart the ones it wantrs in the
new OS.

Cheers,

Tim.

> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
>  xen/common/event_channel.c | 52 
> +++++++++++++++++++++++++++-------------------
>  xen/include/xen/event.h    |  3 +++
>  xen/include/xen/sched.h    |  1 +
>  3 files changed, 35 insertions(+), 21 deletions(-)
> 
> diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
> index fae242d..3204c74 100644
> --- a/xen/common/event_channel.c
> +++ b/xen/common/event_channel.c
> @@ -274,11 +274,13 @@ static long 
> evtchn_bind_interdomain(evtchn_bind_interdomain_t *bind)
>  
>      lchn->u.interdomain.remote_dom  = rd;
>      lchn->u.interdomain.remote_port = rport;
> +    lchn->u.interdomain.opened_by   = current->domain;
>      lchn->state                     = ECS_INTERDOMAIN;
>      evtchn_port_init(ld, lchn);
>      
>      rchn->u.interdomain.remote_dom  = ld;
>      rchn->u.interdomain.remote_port = lport;
> +    rchn->u.interdomain.opened_by   = current->domain;
>      rchn->state                     = ECS_INTERDOMAIN;
>  
>      /*
> @@ -933,26 +935,30 @@ int evtchn_unmask(unsigned int port)
>  }
>  
>  
> -static long evtchn_reset(evtchn_reset_t *r)
> +void evtchn_reset(struct domain *d, bool_t soft_reset)
>  {
> -    domid_t dom = r->dom;
> -    struct domain *d;
> -    int i, rc;
> -
> -    d = rcu_lock_domain_by_any_id(dom);
> -    if ( d == NULL )
> -        return -ESRCH;
> -
> -    rc = xsm_evtchn_reset(XSM_TARGET, current->domain, d);
> -    if ( rc )
> -        goto out;
> +    int i;
> +    struct evtchn *chn;
>  
> +    /*
> +     * ECS_INTERDOMAIN channels with port number suitable for the 2-level ABI
> +     * opened by other domains should remain opened as the domain doing soft
> +     * reset won't be able to reopen them.
> +     * __evtchn_close() also leaves consumer_is_xen() channels open.
> +     */
>      for ( i = 0; port_is_valid(d, i); i++ )
> +    {
> +        chn = evtchn_from_port(d, i);
> +        if ( !soft_reset ||
> +             i >= (BITS_PER_EVTCHN_WORD(d) * BITS_PER_EVTCHN_WORD(d)) ||
> +             chn->state != ECS_INTERDOMAIN ||
> +             chn->u.interdomain.opened_by == d )
>          (void)__evtchn_close(d, i);
> +    }
>  
>      spin_lock(&d->event_lock);
>  
> -    if ( (dom == DOMID_SELF) && d->evtchn_fifo )
> +    if ( (d == current->domain) && d->evtchn_fifo )
>      {
>          /*
>           * Guest domain called EVTCHNOP_reset with DOMID_SELF, destroying
> @@ -964,13 +970,6 @@ static long evtchn_reset(evtchn_reset_t *r)
>      }
>  
>      spin_unlock(&d->event_lock);
> -
> -    rc = 0;
> -
> -out:
> -    rcu_unlock_domain(d);
> -
> -    return rc;
>  }
>  
>  static long evtchn_set_priority(const struct evtchn_set_priority 
> *set_priority)
> @@ -1097,9 +1096,20 @@ long do_event_channel_op(int cmd, 
> XEN_GUEST_HANDLE_PARAM(void) arg)
>  
>      case EVTCHNOP_reset: {
>          struct evtchn_reset reset;
> +        struct domain *d;
> +
>          if ( copy_from_guest(&reset, arg, 1) != 0 )
>              return -EFAULT;
> -        rc = evtchn_reset(&reset);
> +
> +        d = rcu_lock_domain_by_any_id(reset.dom);
> +        if ( d == NULL )
> +            return -ESRCH;
> +
> +        rc = xsm_evtchn_reset(XSM_TARGET, current->domain, d);
> +        if ( !rc )
> +            evtchn_reset(d, 0);
> +
> +        rcu_unlock_domain(d);
>          break;
>      }
>  
> diff --git a/xen/include/xen/event.h b/xen/include/xen/event.h
> index 690f865..d0479a6 100644
> --- a/xen/include/xen/event.h
> +++ b/xen/include/xen/event.h
> @@ -130,6 +130,9 @@ void evtchn_check_pollers(struct domain *d, unsigned int 
> port);
>  
>  void evtchn_2l_init(struct domain *d);
>  
> +/* Close all event channels and reset to 2-level ABI */
> +void evtchn_reset(struct domain *d, bool_t soft_reset);
> +
>  /*
>   * Low-level event channel port ops.
>   */
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index 80c6f62..13b6b86 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -98,6 +98,7 @@ struct evtchn
>          struct {
>              evtchn_port_t  remote_port;
>              struct domain *remote_dom;
> +            struct domain *opened_by;
>          } interdomain; /* state == ECS_INTERDOMAIN */
>          struct {
>              u32            irq;
> -- 
> 1.9.3
> 

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