[PATCH] powerpc: Make cpu_spec __ro_after_init

Michael Ellerman mpe at ellerman.id.au
Wed Oct 25 12:24:52 AEDT 2023

The cpu_spec is a struct holding various information about the CPU the
kernel is executing on. It's populated early in boot and must not change
after that.

In particular the cpu_features and mmu_features hold the set of
discovered CPU/MMU features and are used to set static keys for each
feature, and do binary patching of assembly. So any change to the
cpu_features/mmu_features later in boot will not be reflected in
the state of the static keys or patched code.

There is already logic to check that cpu_features/mmu_features don't
change, see check_features() in feature-fixups.c.

But as another layer of protection the entire cpu_spec should be read
only after init, annotate it as such.

Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
 arch/powerpc/kernel/cputable.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index e97a0fd0ae90..c6678c91401b 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c
@@ -20,9 +20,9 @@
 #include <asm/setup.h>
 #include <asm/cpu_setup.h>
-static struct cpu_spec the_cpu_spec __read_mostly;
+static struct cpu_spec the_cpu_spec __ro_after_init;
-struct cpu_spec* cur_cpu_spec __read_mostly = NULL;
+struct cpu_spec* cur_cpu_spec __ro_after_init = NULL;
 /* The platform string corresponding to the real PVR */

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