x86/sev: Disable KMSAN for memory encryption TUs

Instrumenting sev.c and mem_encrypt_identity.c with KMSAN will result in
a triple-faulting kernel. Some of the code is invoked too early during
boot, before KMSAN is ready.

Disable KMSAN instrumentation for the two translation units.

  [ bp: Massage commit message. ]
Signed-off-by: Changbin Du <changbin.du@huawei.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240308044401.1120395-1-changbin.du@huawei.com

arch/x86/kernel/Makefile

@@ -33,6 +33,7 @@ KASAN_SANITIZE_sev.o					:= n
 KCSAN_SANITIZE := n
 KMSAN_SANITIZE_head$(BITS).o				:= n
 KMSAN_SANITIZE_nmi.o					:= n
+KMSAN_SANITIZE_sev.o					:= n
 
 # If instrumentation of the following files is enabled, boot hangs during
 # first second.

arch/x86/mm/Makefile

@@ -16,6 +16,7 @@ KASAN_SANITIZE_pgprot.o		:= n
 KCSAN_SANITIZE := n
 # Avoid recursion by not calling KMSAN hooks for CEA code.
 KMSAN_SANITIZE_cpu_entry_area.o := n
+KMSAN_SANITIZE_mem_encrypt_identity.o := n
 
 ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_mem_encrypt.o		= -pg