arch/aarch64: Setup SIMD at startup

A recent GRUB binary implicitly uses advanced SIMD registers. We don't
want to trap use of these registers, we have to ensure that
CPACR_EL.FPEN is set to 0b11.

Signed-off-by: Akira Moroo <retrage01@gmail.com>

src/arch/aarch64/mod.rs

@@ -5,4 +5,5 @@
 pub mod asm;
 pub mod layout;
 pub mod paging;
+pub mod simd;
 mod translation;

src/arch/aarch64/simd.rs

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright (C) 2023 Akira Moroo
+
+use aarch64_cpu::registers::*;
+use tock_registers::interfaces::ReadWriteable;
+
+pub fn setup_simd() {
+    CPACR_EL1.modify(CPACR_EL1::FPEN::TrapNothing);
+}

src/main.rs

@@ -171,6 +171,7 @@ pub extern "C" fn rust64_start(#[cfg(not(feature = "coreboot"))] pvh_info: &pvh:
 pub extern "C" fn rust64_start(x0: *const u8) -> ! {
     serial::PORT.borrow_mut().init();
 
+    arch::aarch64::simd::setup_simd();
     arch::aarch64::paging::setup();
 
     let info = fdt::StartInfo::new(x0);