tool: loader map spin table page for BCM2711

The previous commit restricts the loader to only mapping
itself rather than the first 1GB of memory. This is fine
for most platforms as the only other thing they need to
access is the UART which is now also separately mapped in.

The one exception is the BCM2711/Raspberry Pi 4B where the
a spin table is used for SMP booting which is located in
the first page of memory, so we need to explicitly map
that in as well.

This code is a bit of hack since it assumes the CPU release
addrs are always in the first 2MB of memory but the only
platform we have right now that uses spin tables is the
Raspberry Pi 4B.

So we can merge the previous patch, we add this so that we
don't have to regress the Raspberry Pi 4B.

Signed-off-by: Ivan Velickovic <i.velickovic@unsw.edu.au>

Author: Ivan-Velickovic

tool/microkit/src/loader.rs

@@ -547,6 +547,23 @@ impl<'a> Loader<'a> {
             boot_lvl2_lower[start..end].copy_from_slice(&pt_entry.to_le_bytes());
         }
 
+        // TODO: this is a complete hack specific to BCM2711/Raspberry Pi 4B and
+        // will be removed with patches that re-do this loader mapping code.
+        if elf.find_symbol("cpus_release_addr").is_ok() {
+            let lvl2_idx = Aarch64::lvl2_index(0);
+            // Make sure we don't override the loader mappings done above.
+            assert!(Aarch64::lvl2_index(start_addr) != lvl2_idx);
+            assert!(Aarch64::lvl1_index(start_addr) == Aarch64::lvl1_index(0));
+            #[allow(clippy::identity_op)] // keep the (0 << 2) for clarity
+            let pt_entry: u64 = ((lvl2_idx as u64) << AARCH64_2MB_BLOCK_BITS) |
+                (1 << 10) | // access flag
+                (0 << 2) | // strongly ordered memory
+                (1 << 0); // 2M block
+            let start = 8 * lvl2_idx;
+            let end = 8 * (lvl2_idx + 1);
+            boot_lvl2_lower[start..end].copy_from_slice(&pt_entry.to_le_bytes());
+        }
+
         let boot_lvl0_upper: [u8; PAGE_TABLE_SIZE] = [0; PAGE_TABLE_SIZE];
         {
             let pt_entry = (boot_lvl1_upper_addr | 3).to_le_bytes();