In commit f37a59813979, the arguments to add_ext_regions() were switched
from addresses to frame numbers. add_ext_regions() converts the frame
numbers back 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: f37a59813979 ("xen/arm: domain_build: Track unallocated pages using the frame number")
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 270a6b97e42c..2f655bcc2237 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -864,7 +864,7 @@ int __init add_ext_regions(unsigned long s_gfn, unsigned long e_gfn,
     struct membanks *ext_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;
 
     if ( ext_regions->nr_banks >= ext_regions->max_banks )
         return 0;
-- 
2.49.0

On 05/05/2025 04:56, Stewart Hildebrand wrote:
> In commit f37a59813979, the arguments to add_ext_regions() were switched
> from addresses to frame numbers. add_ext_regions() converts the frame
> numbers back 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: f37a59813979 ("xen/arm: domain_build: Track unallocated pages using the frame number")
> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Acked-by: Michal Orzel <michal.orzel@amd.com>

~Michal