diff --git a/lisa/_assets/kmodules/lisa/Makefile b/lisa/_assets/kmodules/lisa/Makefile
index 857ef2eb4f8ae5101124a811e83d06f0e6e5fa04..17b972429e27c447bfeaca8384c1d558fbc30c7c 100644
--- a/lisa/_assets/kmodules/lisa/Makefile
+++ b/lisa/_assets/kmodules/lisa/Makefile
@@ -32,6 +32,15 @@ clean-files := $(GENERATED)
 RUST_VERSION ?= nightly
 RUSTFLAGS := -Clinker=rust-lld -Clink-self-contained=y -Clto=n -Crelocation-model=static -Cno-redzone=y -Ctarget-cpu=generic -Cforce-frame-pointers=y -Ccodegen-units=1 -Zfunction-sections=y
 
+# For now, simply make Rust transparent wrt to the shadow callstack:
+# https://doc.rust-lang.org/beta/unstable-book/compiler-flags/fixed-x18.html
+ifeq ($(ARCH),arm64)
+    ifneq ($(CONFIG_SHADOW_CALL_STACK),)
+        RUSTFLAGS += -Zfixed-x18
+    endif
+endif
+
+
 LISA_EVAL_C := $(MODULE_SRC)/lisa-eval-c.sh
 
 RUSTUP_HOME ?= $(HOME)/.rustup
diff --git a/lisa/_assets/kmodules/lisa/lisa-eval-c.sh b/lisa/_assets/kmodules/lisa/lisa-eval-c.sh
index 7126f1a6b9f678d8b5d9034748e820d915f7a876..687ac9e35f81723252dc8e672ae7123eff895a66 100755
--- a/lisa/_assets/kmodules/lisa/lisa-eval-c.sh
+++ b/lisa/_assets/kmodules/lisa/lisa-eval-c.sh
@@ -21,9 +21,11 @@ trap cleanup EXIT
 # extract the symbol size from the symbol table after compiling. This is works
 # reliably on any compiler and provides the value in hex format.
 
+# We add +1 to the expression, as symbol size for a zero-sized array seems to
+# be 1 weirdly enough. That +1 is then substracted in the awk post-processing
 cat > $src << EOM
 $c_headers
-static char __attribute__((used)) LISA_C_CONST_VALUE[$c_expr];
+static char __attribute__((used)) LISA_C_CONST_VALUE[($c_expr) + 1];
 EOM
 
 CC=${CC:=cc}
@@ -54,5 +56,5 @@ fi
 
 # All -I are relative to the kernel tree root, so we need to run from there.
 cd "$KERNEL_SRC" &&
-$CC $LISA_EVAL_C_CFLAGS "${clang_args[@]}" -c "$src" -o "$object" && $NM -S "$object" | awk '{if ($4 == "LISA_C_CONST_VALUE") {print "0x" $2}}'
+$CC $LISA_EVAL_C_CFLAGS "${clang_args[@]}" -c "$src" -o "$object" && $NM -S "$object" | awk '{if ($4 == "LISA_C_CONST_VALUE")  {print strtonum("0x" $2) - 1}}'
 
diff --git a/lisa/_assets/kmodules/lisa/rust/lisakmod/src/lib.rs b/lisa/_assets/kmodules/lisa/rust/lisakmod/src/lib.rs
index 226e0bea73d61f9ccef10ec5bd05624428b74464..fc30807c768f007d54874b5bf7fc7a30412d498e 100644
--- a/lisa/_assets/kmodules/lisa/rust/lisakmod/src/lib.rs
+++ b/lisa/_assets/kmodules/lisa/rust/lisakmod/src/lib.rs
@@ -1,7 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #![no_std]
 #![no_builtins]
-#![feature(once_cell_try)]
 #![feature(adt_const_params)]
 #![feature(maybe_uninit_fill)]
 #![feature(coerce_unsized)]
diff --git a/lisa/_kmod.py b/lisa/_kmod.py
index d5ac168c250d204f7f0260efe6169a3d2c451f7d..d20da9909ecb2c5f5ec327bfeb80e350cbfa420e 100644
--- a/lisa/_kmod.py
+++ b/lisa/_kmod.py
@@ -189,7 +189,7 @@ class KmodVersionError(Exception):
     pass
 
 
-_ALPINE_DEFAULT_VERSION = '3.20.3'
+_ALPINE_DEFAULT_VERSION = '3.21.3'
 _ALPINE_ROOTFS_URL = 'https://dl-cdn.alpinelinux.org/alpine/v{minor}/releases/{arch}/alpine-minirootfs-{version}-{arch}.tar.gz'
 _ALPINE_PACKAGE_INFO_URL = 'https://pkgs.alpinelinux.org/package/v{version}/{repo}/{arch}/{package}'
 
@@ -2448,6 +2448,7 @@ class _KernelBuildEnv(Loggable, SerializeViaConstructor):
                         checksum=dir_cache.get_key_token(key),
                     )
             else:
+                logger.debug(f'Kernel tree prepare step will not be cached as no cache key could be computed for it.')
                 with _overlay_folders([base_path], backend=overlay_backend, copy_filter=copy_filter) as path:
                     prepare_overlay(path)
                     yield dict(
@@ -2466,15 +2467,17 @@ class _KernelBuildEnv(Loggable, SerializeViaConstructor):
                     repo_root = git.find_root(tree_path)
                     sha1 = git.get_sha1(tree_path)
                     patch = git.get_uncommitted_patch(tree_path)
-                except (FileNotFoundError, subprocess.CalledProcessError):
-                    key = None
+                except (FileNotFoundError, subprocess.CalledProcessError) as e:
+                    logger.debug(f'Could not compute a cache key for kernel tree at {tree_path}: ({e.__class__.__qualname__}) {e}')
+                    tree_key = None
                 else:
                     if repo_root.resolve() == Path(tree_path).resolve():
                         patch_sha1 = hashlib.sha1(patch.encode()).hexdigest()
-                        key = f'{sha1}-{patch_sha1}'
+                        tree_key = ('checksum', f'{sha1}-{patch_sha1}')
                     else:
-                        key = None
-                yield (tree_path, key)
+                        logger.debug(f'Could not compute a cache key for kernel tree at {tree_path} as the root of the kernel tree is not the root of a git repository')
+                        tree_key = None
+                yield (tree_path, tree_key)
             elif version is None:
                 raise ValueError('Kernel version is required in order to download the kernel sources')
             elif cache:
@@ -2488,13 +2491,13 @@ class _KernelBuildEnv(Loggable, SerializeViaConstructor):
                 # Assume that the URL will always provide the same tarball
                 yield (
                     dir_cache.get_entry(url),
-                    url,
+                    ('url', url),
                 )
             else:
                 with tempfile.TemporaryDirectory() as path:
                     yield (
                         cls._make_tree(version, path),
-                        version,
+                        ('version', version),
                     )
 
         cm = chain_cm(overlay_cm, tree_cm)