Re: [Xen-devel] [RFC for-4.5 01/12] xen/common: grant-table: only call IOMMU if paging mode translate is disabled

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.02.14 at 18:43, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> From Xen point of view, ARM guests are PV guest with paging auto translate
> enabled.
> 
> When IOMMU support will be added for ARM, mapping grant ref will always 
> crash
> Xen due to the BUG_ON in __gnttab_map_grant_ref.
> 
> On x86:
>     - PV guests always have paging mode translate disabled
>     - PVH and HVM guests have always paging mode translate enabled
> 
> It means that we can safely replace the check that the domain is a PV guests
> by checking if the guest has paging mode translate enabled.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

> Cc: Keir Fraser <keir@xxxxxxx>
> ---
>  xen/common/grant_table.c |    7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
> index 107b000..778bdb7 100644
> --- a/xen/common/grant_table.c
> +++ b/xen/common/grant_table.c
> @@ -721,12 +721,10 @@ __gnttab_map_grant_ref(
>  
>      double_gt_lock(lgt, rgt);
>  
> -    if ( is_pv_domain(ld) && need_iommu(ld) )
> +    if ( !paging_mode_translate(ld) && need_iommu(ld) )
>      {
>          unsigned int wrc, rdc;
>          int err = 0;
> -        /* Shouldn't happen, because you can't use iommu in a HVM domain. */
> -        BUG_ON(paging_mode_translate(ld));
>          /* We're not translated, so we know that gmfns and mfns are
>             the same things, so the IOMMU entry is always 1-to-1. */
>          mapcount(lgt, rd, frame, &wrc, &rdc);
> @@ -931,11 +929,10 @@ __gnttab_unmap_common(
>              act->pin -= GNTPIN_hstw_inc;
>      }
>  
> -    if ( is_pv_domain(ld) && need_iommu(ld) )
> +    if ( !paging_mode_translate(ld) && need_iommu(ld) )
>      {
>          unsigned int wrc, rdc;
>          int err = 0;
> -        BUG_ON(paging_mode_translate(ld));
>          mapcount(lgt, rd, op->frame, &wrc, &rdc);
>          if ( (wrc + rdc) == 0 )
>              err = iommu_unmap_page(ld, op->frame);
> -- 
> 1.7.10.4
> 
> 
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> http://lists.xen.org/xen-devel 




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