[RFC PATCH v3 12/20] x86: Decrypt trampoline area if memory encryption is active

[Tom Lendacky <thomas.lendacky@amd.com>]

When Secure Memory Encryption is enabled, the trampoline area must not
be encrypted. A CPU running in real mode will not be able to decrypt
memory that has been encrypted because it will not be able to use addresses
with the memory encryption mask.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 arch/x86/realmode/init.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index 5db706f1..44ed32a 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -6,6 +6,7 @@
 #include <asm/pgtable.h>
 #include <asm/realmode.h>
 #include <asm/tlbflush.h>
+#include <asm/mem_encrypt.h>
 
 struct real_mode_header *real_mode_header;
 u32 *trampoline_cr4_features;
@@ -130,6 +131,14 @@ static void __init set_real_mode_permissions(void)
 	unsigned long text_start =
 		(unsigned long) __va(real_mode_header->text_start);
 
+	/*
+	 * If memory encryption is active, the trampoline area will need to
+	 * be in un-encrypted memory in order to bring up other processors
+	 * successfully.
+	 */
+	sme_early_mem_dec(__pa(base), size);
+	sme_set_mem_unenc(base, size);
+
 	set_memory_nx((unsigned long) base, size >> PAGE_SHIFT);
 	set_memory_ro((unsigned long) base, ro_size >> PAGE_SHIFT);
 	set_memory_x((unsigned long) text_start, text_size >> PAGE_SHIFT);