Re: [PATCH v3 20/23] xen/arm: vIOMMU: Modify the partial device tree for dom0less

[Luca Fancellu <Luca.Fancellu@xxxxxxx>]

Hi Milan,

> On 31 Mar 2026, at 02:52, Milan Djokic <milan_djokic@xxxxxxxx> wrote:
> 
> From: Rahul Singh <rahul.singh@xxxxxxx>
> 
> To configure IOMMU in guest for passthrough devices, user will need to
> copy the unmodified "iommus" property from host device tree to partial
> device tree. To enable the dom0 linux kernel to confiure the IOMMU

typo s/confiure/configure/

> correctly replace the phandle in partial device tree with virtual
> IOMMU phandle when "iommus" property is set.
> 
> Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
> Signed-off-by: Milan Djokic <milan_djokic@xxxxxxxx>
> ---
> xen/common/device-tree/dom0less-build.c | 31 ++++++++++++++++++++++++-
> 1 file changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/common/device-tree/dom0less-build.c 
> b/xen/common/device-tree/dom0less-build.c
> index 840d14419d..4b74d2f705 100644
> --- a/xen/common/device-tree/dom0less-build.c
> +++ b/xen/common/device-tree/dom0less-build.c
> @@ -318,7 +318,35 @@ static int __init handle_prop_pfdt(struct kernel_info 
> *kinfo,
>     return ( propoff != -FDT_ERR_NOTFOUND ) ? propoff : 0;
> }
> 
> -static int __init scan_pfdt_node(struct kernel_info *kinfo, const void *pfdt,
> +static void modify_pfdt_node(void *pfdt, int nodeoff)
> +{
> +    int proplen, i, rc;
> +    const fdt32_t *prop;
> +    fdt32_t *prop_c;
> +
> +    prop = fdt_getprop(pfdt, nodeoff, "iommus", &proplen);
> +    if ( !prop )
> +        return;
> +
> +    prop_c = xzalloc_bytes(proplen);

we should check if the allocation was ok

> +
> +    for ( i = 0; i < proplen / 8; ++i )
> +    {
> +        prop_c[i * 2] = cpu_to_fdt32(GUEST_PHANDLE_VSMMUV3);
> +        prop_c[i * 2 + 1] = prop[i * 2 + 1];
> +    }
> +
> +    rc = fdt_setprop(pfdt, nodeoff, "iommus", prop_c, proplen);
> +    if ( rc )
> +    {
> +        dprintk(XENLOG_ERR, "Can't set the iommus property in partial FDT");
> +        return;
> +    }
> +
> +    return;
> +}
> +
> +static int __init scan_pfdt_node(struct kernel_info *kinfo, void *pfdt,
>                                  int nodeoff,
>                                  uint32_t address_cells, uint32_t size_cells,
>                                  bool scan_passthrough_prop)
> @@ -344,6 +372,7 @@ static int __init scan_pfdt_node(struct kernel_info 
> *kinfo, const void *pfdt,
>     node_next = fdt_first_subnode(pfdt, nodeoff);
>     while ( node_next > 0 )
>     {
> +        modify_pfdt_node(pfdt, node_next);
>         rc = scan_pfdt_node(kinfo, pfdt, node_next, address_cells, size_cells,
>                             scan_passthrough_prop);
>         if ( rc )
> 

Cheers,
Luca