Re: [PATCH v3 1/2] xen/arm: exclude xen,reg from direct-map domU extended regions

["Orzel, Michal" <michal.orzel@amd.com>]

On 13/05/2025 21:54, Stewart Hildebrand wrote:
> Similarly to fba1b0974dd8, when a device is passed through to a
> direct-map dom0less domU, the xen,reg ranges may overlap with the
> extended regions. Remove xen,reg from direct-map domU extended regions.
> 
> Introduce rangeset_count_ranges().
> 
> Take the opportunity to update the comment ahead of find_memory_holes().
> 
> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
> ---
> v2->v3:
> * new patch
> ---
>  xen/arch/arm/domain_build.c | 57 +++++++++++++++++++++++++++++++++----
>  xen/common/rangeset.c       | 14 +++++++++
>  xen/include/xen/rangeset.h  |  2 ++
>  3 files changed, 68 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index b189a7cfae9f..3cdf5839bc98 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -824,15 +824,17 @@ static int __init handle_pci_range(const struct dt_device_node *dev,
>  }
>  
>  /*
> - * Find the holes in the Host DT which can be exposed to Dom0 as extended
> - * regions for the special memory mappings. In order to calculate regions
> - * we exclude every addressable memory region described by "reg" and "ranges"
> - * properties from the maximum possible addressable physical memory range:
> + * Find the holes in the Host DT which can be exposed to Dom0 or a direct-map
> + * domU as extended regions for the special memory mappings. In order to
> + * calculate regions we exclude every addressable memory region described by
> + * "reg" and "ranges" properties from the maximum possible addressable physical
> + * memory range:
>   * - MMIO
>   * - Host RAM
>   * - PCI aperture
>   * - Static shared memory regions, which are described by special property
>   *   "xen,shared-mem"
> + * - xen,reg mappings
>   */
>  static int __init find_memory_holes(const struct kernel_info *kinfo,
>                                      struct membanks *ext_regions)
> @@ -914,6 +916,13 @@ static int __init find_memory_holes(const struct kernel_info *kinfo,
>          }
>      }
>  
> +    if ( kinfo->xen_reg_assigned )
> +    {
> +        res = rangeset_subtract(mem_holes, kinfo->xen_reg_assigned);
> +        if ( res )
> +            goto out;
> +    }
> +
>      start = 0;
>      end = (1ULL << p2m_ipa_bits) - 1;
>      res = rangeset_report_ranges(mem_holes, PFN_DOWN(start), PFN_DOWN(end),
> @@ -994,11 +1003,30 @@ static int __init find_domU_holes(const struct kernel_info *kinfo,
>      return res;
>  }
>  
> +static int __init rangeset_to_membank(unsigned long s_gfn, unsigned long e_gfn,
> +                                      void *data)
> +{
> +    struct membanks *membank = data;
> +    paddr_t s = pfn_to_paddr(s_gfn);
> +    paddr_t e = pfn_to_paddr(e_gfn + 1) - 1;
> +
> +    if ( membank->nr_banks >= membank->max_banks )
> +        return 0;
> +
> +    membank->bank[membank->nr_banks].start = s;
> +    membank->bank[membank->nr_banks].size = e - s + 1;
> +    membank->nr_banks++;
> +
> +    return 0;
> +}
> +
>  static int __init find_host_extended_regions(const struct kernel_info *kinfo,
>                                               struct membanks *ext_regions)
>  {
>      int res;
>      struct membanks *gnttab = membanks_xzalloc(1, MEMORY);
> +    struct membanks *xen_reg = membanks_xzalloc(
> +        max(1, rangeset_count_ranges(kinfo->xen_reg_assigned)), MEMORY);
You allocate at least 1 membank even though xen_reg_assigned may be empty because:
 - this function is called for hwdom - no xen,reg
 - there may be no xen,reg i.e. no passthrough

~Michal