[RFC PATCH v4 21/28] x86: Check for memory encryption on the APs

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

Add support to check if memory encryption is active in the kernel and that
it has been enabled on the AP. If memory encryption is active in the kernel
but has not been enabled on the AP, then set the SYS_CFG MSR bit to enable
memory encryption on that AP and allow the AP to continue start up.

Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
 arch/x86/include/asm/realmode.h      |   12 ++++++++++++
 arch/x86/realmode/init.c             |    4 ++++
 arch/x86/realmode/rm/trampoline_64.S |   17 +++++++++++++++++
 3 files changed, 33 insertions(+)

diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
index 230e190..4f7ef53 100644
--- a/arch/x86/include/asm/realmode.h
+++ b/arch/x86/include/asm/realmode.h
@@ -1,6 +1,15 @@
 #ifndef _ARCH_X86_REALMODE_H
 #define _ARCH_X86_REALMODE_H
 
+/*
+ * Flag bit definitions for use with the flags field of the trampoline header
+ * int the CONFIG_X86_64 variant.
+ */
+#define TH_FLAGS_SME_ACTIVE_BIT		0
+#define TH_FLAGS_SME_ACTIVE		BIT(TH_FLAGS_SME_ACTIVE_BIT)
+
+#ifndef __ASSEMBLY__
+
 #include <linux/types.h>
 #include <asm/io.h>
 
@@ -38,6 +47,7 @@ struct trampoline_header {
 	u64 start;
 	u64 efer;
 	u32 cr4;
+	u32 flags;
 #endif
 };
 
@@ -69,4 +79,6 @@ static inline size_t real_mode_size_needed(void)
 void set_real_mode_mem(phys_addr_t mem, size_t size);
 void reserve_real_mode(void);
 
+#endif /* __ASSEMBLY__ */
+
 #endif /* _ARCH_X86_REALMODE_H */
diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index 21d7506..5010089 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -102,6 +102,10 @@ static void __init setup_real_mode(void)
 	trampoline_cr4_features = &trampoline_header->cr4;
 	*trampoline_cr4_features = mmu_cr4_features;
 
+	trampoline_header->flags = 0;
+	if (sme_active())
+		trampoline_header->flags |= TH_FLAGS_SME_ACTIVE;
+
 	trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd);
 	trampoline_pgd[0] = trampoline_pgd_entry.pgd;
 	trampoline_pgd[511] = init_level4_pgt[511].pgd;
diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
index dac7b20..a88c3d1 100644
--- a/arch/x86/realmode/rm/trampoline_64.S
+++ b/arch/x86/realmode/rm/trampoline_64.S
@@ -30,6 +30,7 @@
 #include <asm/msr.h>
 #include <asm/segment.h>
 #include <asm/processor-flags.h>
+#include <asm/realmode.h>
 #include "realmode.h"
 
 	.text
@@ -92,6 +93,21 @@ ENTRY(startup_32)
 	movl	%edx, %fs
 	movl	%edx, %gs
 
+	/* Check for memory encryption support */
+	bt	$TH_FLAGS_SME_ACTIVE_BIT, pa_tr_flags
+	jnc	.Ldone
+	movl	$MSR_K8_SYSCFG, %ecx
+	rdmsr
+	bts	$MSR_K8_SYSCFG_MEM_ENCRYPT_BIT, %eax
+	jc	.Ldone
+
+	/*
+	 * Memory encryption is enabled but the SME enable bit for this
+	 * CPU has has not been set.  It is safe to set it, so do so.
+	 */
+	wrmsr
+.Ldone:
+
 	movl	pa_tr_cr4, %eax
 	movl	%eax, %cr4		# Enable PAE mode
 
@@ -147,6 +163,7 @@ GLOBAL(trampoline_header)
 	tr_start:		.space	8
 	GLOBAL(tr_efer)		.space	8
 	GLOBAL(tr_cr4)		.space	4
+	GLOBAL(tr_flags)	.space	4
 END(trampoline_header)
 
 #include "trampoline_common.S"

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