Re: [PATCH v2 2/3] xen/arm: dom0less: Add trap-unmapped-accesses

[Julien Grall <julien@xxxxxxx>]

Hi Edgar,

On 29/05/2025 16:50, 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 | 9 +++++++++
>   xen/arch/arm/dom0less-build.c         | 9 ++++++++-
>   2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/docs/misc/arm/device-tree/booting.txt 
> b/docs/misc/arm/device-tree/booting.txt
> index 59fa96a82e..8a5c40ddf3 100644
> --- a/docs/misc/arm/device-tree/booting.txt
> +++ b/docs/misc/arm/device-tree/booting.txt
> @@ -225,6 +225,15 @@ 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 0xFFFFFFFF and writes will be 
> ignored.
Looking at the code, if I am not mistaken, it will only return this 
value for 32-bit. For 64-bit there will be a few Fs more and for less 
there will be less. So I think this needs to be reworded.
The rest looks good to me.

> +
> +    This option is only implemented for ARM where the default is 1.
> +
>   - 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,
Cheers,

--
Julien Grall