Re: [Xen-devel] [PATCH for-4.12 v2 5/8] xen/arm: Allow a privileged domain to map foreign page from DOMID_XEN

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 20 Dec 2018, Julien Grall wrote:
> For auto-translated domain, the only way to map page to itself is the
                                                 ^ a page           ^ remove


> using foreign map API. The current code does not allow mapping page from
       ^ the

> special page (such as DOMID_XEN).
> 
> As xentrace buffer are shared using DOMID_XEN, it is not possible to use
              ^ buffers

Aside from these:

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> tracing for Arm.
> 
> This could be solved by using the helper get_pg_owner(). This helper will
> be able to get a reference on DOMID_XEN and therefore allow mapping for
> privileged domain.
> 
> This patch replace the call to rcu_lock_domain_by_any_id() with
> get_pg_owner(). For consistency, all the call to rcu_unlock_domain are
> replaced by put_pg_owner().
> 
> Signed-off-by: Julien grall <julien.grall@xxxxxxx>
> Reviewed-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
> 
> ---
>     Changes in v2:
>         - Add Andrii's reviewed-by
> ---
>  xen/arch/arm/mm.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 58f7e54640..49d7a76aa2 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -1233,20 +1233,20 @@ int xenmem_add_to_physmap_one(
>          struct domain *od;
>          p2m_type_t p2mt;
>  
> -        od = rcu_lock_domain_by_any_id(extra.foreign_domid);
> +        od = get_pg_owner(extra.foreign_domid);
>          if ( od == NULL )
>              return -ESRCH;
>  
>          if ( od == d )
>          {
> -            rcu_unlock_domain(od);
> +            put_pg_owner(od);
>              return -EINVAL;
>          }
>  
>          rc = xsm_map_gmfn_foreign(XSM_TARGET, d, od);
>          if ( rc )
>          {
> -            rcu_unlock_domain(od);
> +            put_pg_owner(od);
>              return rc;
>          }
>  
> @@ -1255,21 +1255,21 @@ int xenmem_add_to_physmap_one(
>          page = get_page_from_gfn(od, idx, &p2mt, P2M_ALLOC);
>          if ( !page )
>          {
> -            rcu_unlock_domain(od);
> +            put_pg_owner(od);
>              return -EINVAL;
>          }
>  
>          if ( !p2m_is_ram(p2mt) )
>          {
>              put_page(page);
> -            rcu_unlock_domain(od);
> +            put_pg_owner(od);
>              return -EINVAL;
>          }
>  
>          mfn = page_to_mfn(page);
>          t = (p2mt == p2m_ram_rw) ? p2m_map_foreign_rw : p2m_map_foreign_ro;
>  
> -        rcu_unlock_domain(od);
> +        put_pg_owner(od);
>          break;
>      }
>      case XENMAPSPACE_dev_mmio:
> -- 
> 2.11.0
> 

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