Erroneous logic was duplicated from add_ext_regions() into
add_hwdom_free_regions(). Frame numbers are converted to addresses, but
the end address (e) is rounded down to page size alignment. The logic to
calculate the size assumes e points to the last address, not page,
effectively leading to the region size being erroneously calculated to
be 2M smaller than the actual size of the region.

Fix by adding 1 to the frame number before converting back to address.

Fixes: 02975cc38389 ("xen/arm: permit non direct-mapped Dom0 construction")
Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
---
 xen/arch/arm/domain_build.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 2f655bcc2237..a0f3c074337d 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -905,7 +905,7 @@ static int __init add_hwdom_free_regions(unsigned long s_gfn,
     struct membanks *free_regions = data;
     paddr_t start, size;
     paddr_t s = pfn_to_paddr(s_gfn);
-    paddr_t e = pfn_to_paddr(e_gfn);
+    paddr_t e = pfn_to_paddr(e_gfn + 1) - 1;
     unsigned int i, j;
 
     if ( free_regions->nr_banks >= free_regions->max_banks )
-- 
2.49.0

On 05/05/2025 04:56, Stewart Hildebrand wrote:
> Erroneous logic was duplicated from add_ext_regions() into
> add_hwdom_free_regions(). Frame numbers are converted to addresses, but
> the end address (e) is rounded down to page size alignment. The logic to
> calculate the size assumes e points to the last address, not page,
> effectively leading to the region size being erroneously calculated to
> be 2M smaller than the actual size of the region.
> 
> Fix by adding 1 to the frame number before converting back to address.
> 
> Fixes: 02975cc38389 ("xen/arm: permit non direct-mapped Dom0 construction")
> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Acked-by: Michal Orzel <michal.orzel@amd.com>

~Michal

On 05/05/2025 09:52, Orzel, Michal wrote:
> 
> 
> On 05/05/2025 04:56, Stewart Hildebrand wrote:
>> Erroneous logic was duplicated from add_ext_regions() into
>> add_hwdom_free_regions(). Frame numbers are converted to addresses, but
>> the end address (e) is rounded down to page size alignment. The logic to
>> calculate the size assumes e points to the last address, not page,
>> effectively leading to the region size being erroneously calculated to
>> be 2M smaller than the actual size of the region.
>>
>> Fix by adding 1 to the frame number before converting back to address.
>>
>> Fixes: 02975cc38389 ("xen/arm: permit non direct-mapped Dom0 construction")
>> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
> Acked-by: Michal Orzel <michal.orzel@amd.com>

I wanted to commit your fixes but rebase is required after recent dom0less code
movement. Please do.

~Michal

On 5/8/25 02:56, Orzel, Michal wrote:
> On 05/05/2025 09:52, Orzel, Michal wrote:
>>
>>
>> On 05/05/2025 04:56, Stewart Hildebrand wrote:
>>> Erroneous logic was duplicated from add_ext_regions() into
>>> add_hwdom_free_regions(). Frame numbers are converted to addresses, but
>>> the end address (e) is rounded down to page size alignment. The logic to
>>> calculate the size assumes e points to the last address, not page,
>>> effectively leading to the region size being erroneously calculated to
>>> be 2M smaller than the actual size of the region.
>>>
>>> Fix by adding 1 to the frame number before converting back to address.
>>>
>>> Fixes: 02975cc38389 ("xen/arm: permit non direct-mapped Dom0 construction")
>>> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
>> Acked-by: Michal Orzel <michal.orzel@amd.com>
> 
> I wanted to commit your fixes but rebase is required after recent dom0less code
> movement. Please do.

Yes, I have already rebased locally. I'll send later today. Is it okay
to keep your A-b tag?

On 08/05/2025 12:30, Stewart Hildebrand wrote:
> On 5/8/25 02:56, Orzel, Michal wrote:
>> On 05/05/2025 09:52, Orzel, Michal wrote:
>>>
>>>
>>> On 05/05/2025 04:56, Stewart Hildebrand wrote:
>>>> Erroneous logic was duplicated from add_ext_regions() into
>>>> add_hwdom_free_regions(). Frame numbers are converted to addresses, but
>>>> the end address (e) is rounded down to page size alignment. The logic to
>>>> calculate the size assumes e points to the last address, not page,
>>>> effectively leading to the region size being erroneously calculated to
>>>> be 2M smaller than the actual size of the region.
>>>>
>>>> Fix by adding 1 to the frame number before converting back to address.
>>>>
>>>> Fixes: 02975cc38389 ("xen/arm: permit non direct-mapped Dom0 construction")
>>>> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
>>> Acked-by: Michal Orzel <michal.orzel@amd.com>
>>
>> I wanted to commit your fixes but rebase is required after recent dom0less code
>> movement. Please do.
> 
> Yes, I have already rebased locally. I'll send later today. Is it okay
> to keep your A-b tag?
Yes, of course.

~Michal