x86/microcode: Handle "nosmt" correctly

On CPUs where microcode loading is not NMI-safe the SMT siblings which
are parked in one of the play_dead() variants still react to NMIs.

So if an NMI hits while the primary thread updates the microcode the
resulting behaviour is undefined. The default play_dead() implementation on
modern CPUs is using MWAIT which is not guaranteed to be safe against
a microcode update which affects MWAIT.

Take the cpus_booted_once_mask into account to detect this case and
refuse to load late if the vendor specific driver does not advertise
that late loading is NMI safe.

AMD stated that this is safe, so mark the AMD driver accordingly.

This requirement will be partially lifted in later changes.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231002115903.087472735@linutronix.de

1 files changed, 6 insertions, 7 deletions

diff --git a/arch/x86/kernel/cpu/microcode/internal.h b/arch/x86/kernel/cpu/microcode/internal.h
index 4bef216f8d6c..07aa5f8be69b 100644
--- a/arch/x86/kernel/cpu/microcode/internal.h
+++ b/arch/x86/kernel/cpu/microcode/internal.h
@@ -20,18 +20,17 @@ enum ucode_state {
 
 struct microcode_ops {
 	enum ucode_state (*request_microcode_fw)(int cpu, struct device *dev);
-
 	void (*microcode_fini_cpu)(int cpu);
 
 	/*
-	 * The generic 'microcode_core' part guarantees that
-	 * the callbacks below run on a target cpu when they
-	 * are being called.
+	 * The generic 'microcode_core' part guarantees that the callbacks
+	 * below run on a target CPU when they are being called.
 	 * See also the "Synchronization" section in microcode_core.c.
 	 */
-	enum ucode_state (*apply_microcode)(int cpu);
-	int (*collect_cpu_info)(int cpu, struct cpu_signature *csig);
-	void (*finalize_late_load)(int result);
+	enum ucode_state	(*apply_microcode)(int cpu);
+	int			(*collect_cpu_info)(int cpu, struct cpu_signature *csig);
+	void			(*finalize_late_load)(int result);
+	unsigned int		nmi_safe	: 1;
 };
 
 extern struct ucode_cpu_info ucode_cpu_info[];