Re: [PATCH v3 2/5] xen/arm: dom0less: Add trap-unmapped-accesses

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 30 May 2025, Edgar E. Iglesias wrote:
> From: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxx>
> 
> Add the trap-unmapped-accesses per-domain fdt property.
> 
> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xxxxxxx>
> ---
>  docs/misc/arm/device-tree/booting.txt | 10 ++++++++++
>  xen/arch/arm/dom0less-build.c         |  9 ++++++++-
>  2 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/misc/arm/device-tree/booting.txt 
> b/docs/misc/arm/device-tree/booting.txt
> index 59fa96a82e..9add6440de 100644
> --- a/docs/misc/arm/device-tree/booting.txt
> +++ b/docs/misc/arm/device-tree/booting.txt
> @@ -225,6 +225,16 @@ with the following properties:
>      option is provided with a non zero value, but the platform doesn't 
> support
>      SVE.
>  
> +- trap-unmapped-accesses
> +
> +    Optional. An integer that configures handling of accesses to unmapped
> +    address ranges.
> +    If set to 0, guest accesses will read all bits as ones, e.g 0xFFFFFFFF
> +    for a 32bit access and writes will be ignored.
> +    If set to 1, guest accesses will trap.
> +
> +    This option is only implemented for ARM where the default is 1.

Please expand it to: "This option is only implemented for ARM where the
default is 1 when trap-unmapped-accesses is absent."

The change could be done on commit:

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


>  - xen,enhanced
>  
>      A string property. Possible property values are:
> diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
> index a4e0a33632..69324aa597 100644
> --- a/xen/arch/arm/dom0less-build.c
> +++ b/xen/arch/arm/dom0less-build.c
> @@ -344,8 +344,15 @@ void __init arch_create_domUs(struct dt_device_node 
> *node,
>  #endif
>      }
>  
> -    /* Trap accesses to unmapped areas. */
> +    /* Trap unmapped accesses by default. */
>      d_cfg->flags |= XEN_DOMCTL_CDF_trap_unmapped_accesses;
> +    if ( dt_property_read_u32(node, "trap-unmapped-accesses", &val) )
> +    {
> +        if ( val > 1 )
> +            panic("trap-unmapped-accesses: supported values are 0 or 1");
> +        if ( !val )
> +            d_cfg->flags &= ~XEN_DOMCTL_CDF_trap_unmapped_accesses;
> +    }
>  }
>  
>  int __init init_intc_phandle(struct kernel_info *kinfo, const char *name,
> -- 
> 2.43.0
>