Re: [Xen-devel] [PATCH 08/18] xen: Add DOMID_SELF support to rcu_lock_domain_by_id

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.08.12 at 16:32, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
> Callers that want to prevent use of DOMID_SELF already need to ensure
> the calling domain does not pass its own domain ID. This removes the
> need for the caller to manually support DOMID_SELF, which many already
> do.

I'm not really sure this is correct. At the very least it changes the
return value of rcu_lock_remote_target_domain_by_id() when
called with DOMID_SELF (from -ESRCH to -EPERM).

I'm also not convinced that a distinction between a domain knowing
its ID and one passing DOMID_SELF isn't/can't be useful. That of
course depends on whether the ID can be fully hidden from a guest
(obviously pure HVM guests would never know their ID, but then
again they also would never pass DOMID_SELF anywhere; it might
be, however, that they could get the latter passed on their behalf
e.g. from some emulation function).

Jan

> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> ---
>  xen/common/domain.c        | 3 +++
>  xen/common/event_channel.c | 3 ---
>  xen/common/grant_table.c   | 2 +-
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/common/domain.c b/xen/common/domain.c
> index 4c5d241..dbbc414 100644
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -400,6 +400,9 @@ struct domain *rcu_lock_domain_by_id(domid_t dom)
>  {
>      struct domain *d = NULL;
>  
> +    if ( dom == DOMID_SELF )
> +        return rcu_lock_current_domain();
> +
>      rcu_read_lock(&domlist_read_lock);
>  
>      for ( d = rcu_dereference(domain_hash[DOMAIN_HASH(dom)]);
> diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
> index 53777f8..988d3ce 100644
> --- a/xen/common/event_channel.c
> +++ b/xen/common/event_channel.c
> @@ -201,9 +201,6 @@ static long 
> evtchn_bind_interdomain(evtchn_bind_interdomain_t *bind)
>      domid_t        rdom = bind->remote_dom;
>      long           rc;
>  
> -    if ( rdom == DOMID_SELF )
> -        rdom = current->domain->domain_id;
> -
>      if ( (rd = rcu_lock_domain_by_id(rdom)) == NULL )
>          return -ESRCH;
>  
> diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
> index 9961e83..fbea67c 100644
> --- a/xen/common/grant_table.c
> +++ b/xen/common/grant_table.c
> @@ -715,7 +715,7 @@ __gnttab_map_grant_ref(
>      TRACE_1D(TRC_MEM_PAGE_GRANT_MAP, op->dom);
>  
>      mt = &maptrack_entry(lgt, handle);
> -    mt->domid = op->dom;
> +    mt->domid = rd->domain_id;
>      mt->ref   = op->ref;
>      mt->flags = op->flags;
>  
> -- 
> 1.7.11.2
> 
> 
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> http://lists.xen.org/xen-devel 




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