x86/compressed/acpi: Move EFI system table lookup to helper

Future patches for SEV-SNP-validated CPUID will also require early
parsing of the EFI configuration. Incrementally move the related
code into a set of helpers that can be re-used for that purpose.
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-26-brijesh.singh@amd.com

arch/x86/boot/compressed/acpi.c

@@ -105,7 +105,7 @@ static acpi_physical_address kexec_get_rsdp_addr(void)
 	}
 
 	/* Get systab from boot params. */
-	systab = (efi_system_table_64_t *) (ei->efi_systab | ((__u64)ei->efi_systab_hi << 32));
+	systab = (efi_system_table_64_t *)efi_get_system_table(boot_params);
 	if (!systab)
 		error("EFI system table not found in kexec boot_params.");
 
@@ -118,9 +118,8 @@ static acpi_physical_address kexec_get_rsdp_addr(void) { return 0; }
 static acpi_physical_address efi_get_rsdp_addr(void)
 {
 #ifdef CONFIG_EFI
-	unsigned long systab, config_tables;
+	unsigned long systab_pa, config_tables;
 	unsigned int nr_tables;
-	struct efi_info *ei;
 	enum efi_type et;
 	bool efi_64;
 
@@ -132,24 +131,18 @@ static acpi_physical_address efi_get_rsdp_addr(void)
 	else
 		return 0;
 
-	/* Get systab from boot params. */
-	ei = &boot_params->efi_info;
-#ifdef CONFIG_X86_64
-	systab = ei->efi_systab | ((__u64)ei->efi_systab_hi << 32);
-#else
-	systab = ei->efi_systab;
-#endif
-	if (!systab)
-		error("EFI system table not found.");
+	systab_pa = efi_get_system_table(boot_params);
+	if (!systab_pa)
+		error("EFI support advertised, but unable to locate system table.");
 
 	/* Handle EFI bitness properly */
 	if (efi_64) {
-		efi_system_table_64_t *stbl = (efi_system_table_64_t *)systab;
+		efi_system_table_64_t *stbl = (efi_system_table_64_t *)systab_pa;
 
 		config_tables	= stbl->tables;
 		nr_tables	= stbl->nr_tables;
 	} else {
-		efi_system_table_32_t *stbl = (efi_system_table_32_t *)systab;
+		efi_system_table_32_t *stbl = (efi_system_table_32_t *)systab_pa;
 
 		config_tables	= stbl->tables;
 		nr_tables	= stbl->nr_tables;

arch/x86/boot/compressed/efi.c

@@ -48,3 +48,32 @@ enum efi_type efi_get_type(struct boot_params *bp)
 
 	return et;
 }
+
+/**
+ * efi_get_system_table - Given a pointer to boot_params, retrieve the physical address
+ *                        of the EFI system table.
+ *
+ * @bp:         pointer to boot_params
+ *
+ * Return: EFI system table address on success. On error, return 0.
+ */
+unsigned long efi_get_system_table(struct boot_params *bp)
+{
+	unsigned long sys_tbl_pa;
+	struct efi_info *ei;
+	enum efi_type et;
+
+	/* Get systab from boot params. */
+	ei = &bp->efi_info;
+#ifdef CONFIG_X86_64
+	sys_tbl_pa = ei->efi_systab | ((__u64)ei->efi_systab_hi << 32);
+#else
+	sys_tbl_pa = ei->efi_systab;
+#endif
+	if (!sys_tbl_pa) {
+		debug_putstr("EFI system table not found.");
+		return 0;
+	}
+
+	return sys_tbl_pa;
+}

arch/x86/boot/compressed/misc.h

@@ -185,11 +185,17 @@ enum efi_type {
 #ifdef CONFIG_EFI
 /* helpers for early EFI config table access */
 enum efi_type efi_get_type(struct boot_params *bp);
+unsigned long efi_get_system_table(struct boot_params *bp);
 #else
 static inline enum efi_type efi_get_type(struct boot_params *bp)
 {
 	return EFI_TYPE_NONE;
 }
+
+static inline unsigned long efi_get_system_table(struct boot_params *bp)
+{
+	return 0;
+}
 #endif /* CONFIG_EFI */
 
 #endif /* BOOT_COMPRESSED_MISC_H */