Re: [PATCH v3 1/5] xen/arm: Add way to disable traps on accesses to unmapped addresses

[Julien Grall <julien@xxxxxxx>]

Hi Edgar,

On 30/05/2025 14:45, Edgar E. Iglesias wrote:
> From: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxx>
>
> Add a per-domain way to optionally disable traps for accesses
> to unmapped addresses.
>
> The domain flag is general but it's only implemented for ARM for now.
>
> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xxxxxxx>
> ---
>   tools/libs/light/libxl_arm.c  |  3 +++
>   xen/arch/arm/dom0less-build.c |  3 +++
>   xen/arch/arm/domain.c         |  3 ++-
>   xen/arch/arm/domain_build.c   |  3 ++-
>   xen/arch/arm/io.c             | 37 +++++++++++++++++++++++++++++++++--
>   xen/common/domain.c           |  3 ++-
>   xen/include/public/domctl.h   |  4 +++-
>   7 files changed, 50 insertions(+), 6 deletions(-)
>
> diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
> index 75c811053c..9530996e72 100644
> --- a/tools/libs/light/libxl_arm.c
> +++ b/tools/libs/light/libxl_arm.c
> @@ -233,6 +233,9 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
>           config->arch.sve_vl = d_config->b_info.arch_arm.sve_vl / 128U;
>       }
>   
> +    /* Trap accesses to unmapped areas. */
> +    config->flags |= XEN_DOMCTL_CDF_trap_unmapped_accesses;
> +
>       return 0;
>   }
>   
> diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
> index a49764f0ad..a4e0a33632 100644
> --- a/xen/arch/arm/dom0less-build.c
> +++ b/xen/arch/arm/dom0less-build.c
> @@ -343,6 +343,9 @@ void __init arch_create_domUs(struct dt_device_node *node,
>           panic("'sve' property found, but CONFIG_ARM64_SVE not selected\n");
>   #endif
>       }
> +
> +    /* Trap accesses to unmapped areas. */
> +    d_cfg->flags |= XEN_DOMCTL_CDF_trap_unmapped_accesses;
>   }
>   
>   int __init init_intc_phandle(struct kernel_info *kinfo, const char *name,
> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> index 45aeb8bddc..be58a23dd7 100644
> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -612,7 +612,8 @@ int arch_sanitise_domain_config(struct 
> xen_domctl_createdomain *config)
>       unsigned int max_vcpus;
>       unsigned int flags_required = (XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap);
>       unsigned int flags_optional = (XEN_DOMCTL_CDF_iommu | XEN_DOMCTL_CDF_vpmu 
> |
> -                                   XEN_DOMCTL_CDF_xs_domain );
> +                                   XEN_DOMCTL_CDF_xs_domain |
> +                                   XEN_DOMCTL_CDF_trap_unmapped_accesses );
Just to double check, doesn't this mean the flag will be allowed on x86? 
If so, shouldn't we reject it in an arch?
Cheers,

--
Julien Grall