[PATCH v9 36/43] x86/compressed/64: Add identity mapping for Confidential Computing blob

[Brijesh Singh]

From: Michael Roth <michael.roth@xxxxxxx>

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 the blob and the CPUID
table it points to are mapped in advance.

Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/boot/compressed/ident_map_64.c |  3 ++-
 arch/x86/boot/compressed/misc.h         |  2 ++
 arch/x86/boot/compressed/sev.c          | 22 ++++++++++++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index 7975680f521f..e4b093a0862d 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -163,8 +163,9 @@ void initialize_identity_maps(void *rmode)
 	cmdline = get_cmd_line_ptr();
 	kernel_add_identity_map(cmdline, cmdline + COMMAND_LINE_SIZE);
 
+	sev_prep_identity_maps(top_level_pgt);
+
 	/* Load the new page-table. */
-	sev_verify_cbit(top_level_pgt);
 	write_cr3(top_level_pgt);
 }
 
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index cfa0663bf931..72eda6c26c11 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -127,6 +127,7 @@ void sev_es_shutdown_ghcb(void);
 extern bool sev_es_check_ghcb_fault(unsigned long address);
 void snp_set_page_private(unsigned long paddr);
 void snp_set_page_shared(unsigned long paddr);
+void sev_prep_identity_maps(unsigned long top_level_pgt);
 #else
 static inline void sev_enable(struct boot_params *bp) { }
 static inline void sev_es_shutdown_ghcb(void) { }
@@ -136,6 +137,7 @@ static inline bool sev_es_check_ghcb_fault(unsigned long address)
 }
 static inline void snp_set_page_private(unsigned long paddr) { }
 static inline void snp_set_page_shared(unsigned long paddr) { }
+static inline void sev_prep_identity_maps(unsigned long top_level_pgt) { }
 #endif
 
 /* acpi.c */
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index e1596bfc13e6..faf432684870 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -496,3 +496,25 @@ bool snp_init(struct boot_params *bp)
 	 */
 	return true;
 }
+
+void sev_prep_identity_maps(unsigned long top_level_pgt)
+{
+	/*
+	 * The ConfidentialComputing blob is used very early in uncompressed
+	 * kernel to find the in-memory cpuid table to handle cpuid
+	 * instructions. Make sure an identity-mapping exists so it can be
+	 * accessed after switchover.
+	 */
+	if (sev_snp_enabled()) {
+		unsigned long cc_info_pa = boot_params->cc_blob_address;
+		struct cc_blob_sev_info *cc_info;
+
+		kernel_add_identity_map(cc_info_pa,
+					cc_info_pa + sizeof(*cc_info));
+		cc_info = (struct cc_blob_sev_info *)cc_info_pa;
+		kernel_add_identity_map((unsigned long)cc_info->cpuid_phys,
+					(unsigned long)cc_info->cpuid_phys + cc_info->cpuid_len);
+	}
+
+	sev_verify_cbit(top_level_pgt);
+}
-- 
2.25.1