ACPICA: Revert "ACPICA: avoid Info: mapping multiple BARs. Your kernel is fine."

Undo the modifications made in commit d410ee5 ("ACPICA: avoid
"Info: mapping multiple BARs. Your kernel is fine.""). The initial
purpose of this commit was to stop memory mappings for operation
regions from overlapping page boundaries, as it can trigger warnings
if different page attributes are present.

However, it was found that when this situation arises, mapping
continues until the boundary's end, but there is still an attempt to
read/write the entire length of the map, leading to a NULL pointer
deference. For example, if a four-byte mapping request is made but
only one byte is mapped because it hits the current page boundary's
end, a four-byte read/write attempt is still made, resulting in a NULL
pointer deference.

Instead, map the entire length, as the ACPI specification does not
mandate that it must be within the same page boundary. It is
permissible for it to be mapped across different regions.

Link: acpica/acpica#954
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218849
Fixes: d410ee5 ("ACPICA: avoid "Info: mapping multiple BARs. Your kernel is fine."")
Co-developed-by: Sanath S <[email protected]>
Signed-off-by: Sanath S <[email protected]>
Signed-off-by: Raju Rangoju <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: RajuRangoju

drivers/acpi/acpica/exregion.c

@@ -44,7 +44,6 @@ acpi_ex_system_memory_space_handler(u32 function,
 	struct acpi_mem_mapping *mm = mem_info->cur_mm;
 	u32 length;
 	acpi_size map_length;
-	acpi_size page_boundary_map_length;
 #ifdef ACPI_MISALIGNMENT_NOT_SUPPORTED
 	u32 remainder;
 #endif
@@ -138,26 +137,8 @@ acpi_ex_system_memory_space_handler(u32 function,
 		map_length = (acpi_size)
 		    ((mem_info->address + mem_info->length) - address);
 
-		/*
-		 * If mapping the entire remaining portion of the region will cross
-		 * a page boundary, just map up to the page boundary, do not cross.
-		 * On some systems, crossing a page boundary while mapping regions
-		 * can cause warnings if the pages have different attributes
-		 * due to resource management.
-		 *
-		 * This has the added benefit of constraining a single mapping to
-		 * one page, which is similar to the original code that used a 4k
-		 * maximum window.
-		 */
-		page_boundary_map_length = (acpi_size)
-		    (ACPI_ROUND_UP(address, ACPI_DEFAULT_PAGE_SIZE) - address);
-		if (page_boundary_map_length == 0) {
-			page_boundary_map_length = ACPI_DEFAULT_PAGE_SIZE;
-		}
-
-		if (map_length > page_boundary_map_length) {
-			map_length = page_boundary_map_length;
-		}
+		if (map_length > ACPI_DEFAULT_PAGE_SIZE)
+			map_length = ACPI_DEFAULT_PAGE_SIZE;
 
 		/* Create a new mapping starting at the address given */