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Subject: [PATCH Part1 RFC v4 29/36] x86/compressed/64: add identity mapping for Confidential Computing blob
Date:   Wed,  7 Jul 2021 13:14:59 -0500
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From: Michael Roth <michael.roth@amd.com>

The run-time kernel will need to access the Confidential Computing
blob very early in boot to access the CPUID table it points to. At that
stage of boot it will be relying on the identity-mapped page table set
up by boot/compressed kernel, so make sure we have both of them mapped
in advance.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 arch/x86/boot/compressed/ident_map_64.c | 18 ++++++++++++++++++
 arch/x86/boot/compressed/sev.c          |  2 +-
 arch/x86/include/asm/sev.h              |  8 ++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index 59befc610993..91e5ab433be4 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -37,6 +37,9 @@
 #include <asm/setup.h>	/* For COMMAND_LINE_SIZE */
 #undef _SETUP
 
+#define __BOOT_COMPRESSED
+#include <asm/sev.h> /* For sev_snp_active() + ConfidentialComputing blob */
+
 extern unsigned long get_cmd_line_ptr(void);
 
 /* Used by PAGE_KERN* macros: */
@@ -163,6 +166,21 @@ void initialize_identity_maps(void *rmode)
 	cmdline = get_cmd_line_ptr();
 	add_identity_map(cmdline, cmdline + COMMAND_LINE_SIZE);
 
+	/*
+	 * The ConfidentialComputing blob is used very early in uncompressed
+	 * kernel to find CPUID memory to handle cpuid instructions. Make sure
+	 * an identity-mapping exists so they can be accessed after switchover.
+	 */
+	if (sev_snp_enabled()) {
+		struct cc_blob_sev_info *cc_info =
+			(void *)(unsigned long)boot_params->cc_blob_address;
+
+		add_identity_map((unsigned long)cc_info,
+				 (unsigned long)cc_info + sizeof(*cc_info));
+		add_identity_map((unsigned long)cc_info->cpuid_phys,
+				 (unsigned long)cc_info->cpuid_phys + cc_info->cpuid_len);
+	}
+
 	/* Load the new page-table. */
 	sev_verify_cbit(top_level_pgt);
 	write_cr3(top_level_pgt);
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 13a6ce74f320..87080bc4a574 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -123,7 +123,7 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
 /* Include code for early handlers */
 #include "../../kernel/sev-shared.c"
 
-static inline bool sev_snp_enabled(void)
+bool sev_snp_enabled(void)
 {
 	unsigned long low, high;
 
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index e403bd1fcb23..b5715a26361a 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -128,6 +128,10 @@ void snp_set_memory_shared(unsigned long vaddr, unsigned int npages);
 void snp_set_memory_private(unsigned long vaddr, unsigned int npages);
 void snp_set_wakeup_secondary_cpu(void);
 
+#ifdef __BOOT_COMPRESSED
+bool sev_snp_enabled(void);
+#endif
+
 void sev_snp_cpuid_init(struct boot_params *bp);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
@@ -145,6 +149,10 @@ static inline void snp_set_memory_shared(unsigned long vaddr, unsigned int npage
 static inline void snp_set_memory_private(unsigned long vaddr, unsigned int npages) { }
 static inline void snp_set_wakeup_secondary_cpu(void) { }
 
+#ifdef __BOOT_COMPRESSED
+static inline bool sev_snp_enabled { return false; }
+#endif
+
 static inline void sev_snp_cpuid_init(struct boot_params *bp) { }
 #endif
 
-- 
2.17.1