Re: [XEN PATCH v3] xen/arm: introduce dummy iommu node for dom0

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 11 Jan 2022, Sergiy Kibrik wrote:
> Currently no IOMMU properties are exposed to dom0, thus kernel by default
> assumes no protection and enables swiotlb-xen, which leads to costly and
> unnecessary buffers bouncing.
> 
> To let kernel know which device is behing IOMMU and hence needs no swiotlb
> services we introduce dummy xen-iommu node in FDT and link protected device
> nodes to it, using here device tree iommu bindings.
> 
> Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>

I think the patch looks good. I have no further comments on the code:

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

Before committing it to the Xen tree, I'd like to wait that the Linux
side, especially the change to
Documentation/devicetree/bindings/arm/xen.txt, is acked.


> ---
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien@xxxxxxx>
> Cc: Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>
> Cc: Andrii Anisov <Andrii_Anisov@xxxxxxxx>
> 
> 
> Changelog:
> 
> v3: rebased over staging & remove redundand phandle_iommu attribute, 
> discussion:
>       
> https://lists.xenproject.org/archives/html/xen-devel/2021-12/msg01753.html
> 
> v2: re-use common iommu dt bindings to let guests know which devices are 
> protected:
>       
> https://lists.xenproject.org/archives/html/xen-devel/2021-10/msg00073.html
> 
>  xen/arch/arm/domain_build.c           | 42 +++++++++++++++++++++++++++
>  xen/include/public/device_tree_defs.h |  1 +
>  2 files changed, 43 insertions(+)
> 
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 6931c022a2..b82ba72fac 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -845,6 +845,12 @@ static int __init write_properties(struct domain *d, 
> struct kernel_info *kinfo,
>          }
>      }
>  
> +    if ( iommu_node && is_iommu_enabled(d) && dt_device_is_protected(node) )
> +    {
> +        res = fdt_property_cell(kinfo->fdt, "iommus", GUEST_PHANDLE_IOMMU);
> +        if ( res )
> +            return res;
> +    }
>      return 0;
>  }
>  
> @@ -1479,6 +1485,38 @@ static int __init make_cpus_node(const struct domain 
> *d, void *fdt)
>      return res;
>  }
>  
> +static int __init make_iommu_node(const struct domain *d,
> +                                  const struct kernel_info *kinfo)
> +{
> +    const char compat[] = "xen,iommu-el2-v1";
> +    int res;
> +
> +    if ( !is_iommu_enabled(d) )
> +        return 0;
> +
> +    dt_dprintk("Create iommu node\n");
> +
> +    res = fdt_begin_node(kinfo->fdt, "xen-iommu");
> +    if ( res )
> +        return res;
> +
> +    res = fdt_property(kinfo->fdt, "compatible", compat, sizeof(compat));
> +    if ( res )
> +        return res;
> +
> +    res = fdt_property_cell(kinfo->fdt, "#iommu-cells", 0);
> +    if ( res )
> +        return res;
> +
> +    res = fdt_property_cell(kinfo->fdt, "phandle", GUEST_PHANDLE_IOMMU);
> +
> +    res = fdt_end_node(kinfo->fdt);
> +    if ( res )
> +        return res;
> +
> +    return res;
> +}
> +
>  static int __init make_gic_node(const struct domain *d, void *fdt,
>                                  const struct dt_device_node *node)
>  {
> @@ -2127,6 +2165,10 @@ static int __init handle_node(struct domain *d, struct 
> kernel_info *kinfo,
>          if ( res )
>              return res;
>  
> +        res = make_iommu_node(d, kinfo);
> +        if ( res )
> +            return res;
> +
>          res = make_memory_node(d, kinfo->fdt, addrcells, sizecells, 
> &kinfo->mem);
>          if ( res )
>              return res;
> diff --git a/xen/include/public/device_tree_defs.h 
> b/xen/include/public/device_tree_defs.h
> index 209d43de3f..df58944bd0 100644
> --- a/xen/include/public/device_tree_defs.h
> +++ b/xen/include/public/device_tree_defs.h
> @@ -7,6 +7,7 @@
>   * onwards. Reserve a high value for the GIC phandle.
>   */
>  #define GUEST_PHANDLE_GIC (65000)
> +#define GUEST_PHANDLE_IOMMU (GUEST_PHANDLE_GIC + 1)
>  
>  #define GUEST_ROOT_ADDRESS_CELLS 2
>  #define GUEST_ROOT_SIZE_CELLS 2
> -- 
> 2.25.1
>