Write to lower 1GB of free regions in lower_memory_free test

Author: Wasabi375

tests/test_kernels/lower_memory_free/src/bin/lower_memory_free.rs

@@ -7,6 +7,7 @@ use bootloader_api::{
 use test_kernel_lower_memory_free::{exit_qemu, QemuExitCode};
 
 const LOWER_MEMORY_END_PAGE: u64 = 0x0010_0000;
+const WRITE_TEST_UNTIL: u64 = 0x4000_0000;
 
 pub const BOOTLOADER_CONFIG: BootloaderConfig = {
     let mut config = BootloaderConfig::new_default();
@@ -34,16 +35,17 @@ fn kernel_main(boot_info: &'static mut BootInfo) -> ! {
         .unwrap();
         if region.kind == MemoryRegionKind::Usable && region.start < LOWER_MEMORY_END_PAGE {
             let end = core::cmp::min(region.end, LOWER_MEMORY_END_PAGE);
-
+            let pages = (end - region.start) / 4096;
+            count += pages;
+        }
+        if region.kind == MemoryRegionKind::Usable && region.start < WRITE_TEST_UNTIL {
+            let end = core::cmp::min(region.end, WRITE_TEST_UNTIL);
             // ensure region is actually writable
             let addr = phys_mem_offset + region.start;
             let size = end - region.start;
             unsafe {
                 core::ptr::write_bytes(addr as *mut u8, 0xff, size as usize);
             }
-
-            let pages = (end - region.start) / 4096;
-            count += pages;
         }
     }