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

[Stewart Hildebrand <stewart.hildebrand@xxxxxxx>]

On 5/14/25 03:31, Orzel, Michal wrote:
> 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@xxxxxxx>
>> ---
>> 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

Ah, sorry, there's no need to allocate at least 1. This can just be:

    struct membanks *xen_reg = membanks_xzalloc(
        rangeset_count_ranges(kinfo->arch.xen_reg_assigned), MEMORY);