[PATCH v13 3/6] x86/boot: Introduce efi_get_rsdp_addr() to find RSDP from EFI table

[Chao Fan]

Memory information in SRAT is necessary to fix the conflict between
KASLR and memory-hotremove. So RSDP and SRAT should be parsed.

When booting form KEXEC/EFI/BIOS, the methods to compute RSDP
are different. When booting from EFI, EFI table points to RSDP.
So parse the EFI table and find the RSDP.

Signed-off-by: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
---
 arch/x86/boot/compressed/acpi.c | 79 +++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
index cad15686f82c..c96008712ec9 100644
--- a/arch/x86/boot/compressed/acpi.c
+++ b/arch/x86/boot/compressed/acpi.c
@@ -28,3 +28,82 @@ static acpi_physical_address get_acpi_rsdp(void)
 	return 0;
 #endif
 }
+
+/* Search EFI table for RSDP. */
+static acpi_physical_address efi_get_rsdp_addr(void)
+{
+#ifdef CONFIG_EFI
+	acpi_physical_address rsdp_addr = 0;
+	efi_system_table_t *systab;
+	struct efi_info *e;
+	bool efi_64;
+	char *sig;
+	int size;
+	int i;
+
+	e = &boot_params->efi_info;
+	sig = (char *)&e->efi_loader_signature;
+
+	if (!strncmp(sig, EFI64_LOADER_SIGNATURE, 4))
+		efi_64 = true;
+	else if (!strncmp(sig, EFI32_LOADER_SIGNATURE, 4))
+		efi_64 = false;
+	else {
+		debug_putstr("Wrong EFI loader signature.\n");
+		return 0;
+	}
+
+	/* Get systab from boot params. Based on efi_init(). */
+#ifdef CONFIG_X86_64
+	systab = (efi_system_table_t *)(e->efi_systab | ((__u64)e->efi_systab_hi<<32));
+#else
+	if (e->efi_systab_hi || e->efi_memmap_hi) {
+		debug_putstr("Error getting RSDP address: EFI system table located above 4GB.\n");
+		return 0;
+	}
+	systab = (efi_system_table_t *)e->efi_systab;
+#endif
+
+	if (!systab)
+		return 0;
+
+	/*
+	 * Get EFI tables from systab. Based on efi_config_init() and
+	 * efi_config_parse_tables().
+	 */
+	size = efi_64 ? sizeof(efi_config_table_64_t) :
+			sizeof(efi_config_table_32_t);
+
+	for (i = 0; i < systab->nr_tables; i++) {
+		void *config_tables;
+		unsigned long table;
+		efi_guid_t guid;
+
+		config_tables = (void *)(systab->tables + size * i);
+		if (efi_64) {
+			efi_config_table_64_t *tmp_table;
+
+			tmp_table = (efi_config_table_64_t *)config_tables;
+			guid = tmp_table->guid;
+			table = tmp_table->table;
+
+			if (!IS_ENABLED(CONFIG_X86_64) && table >> 32) {
+				debug_putstr("Error getting RSDP address: EFI system table located above 4GB.\n");
+				return 0;
+			}
+		} else {
+			efi_config_table_32_t *tmp_table;
+
+			tmp_table = (efi_config_table_32_t *)config_tables;
+			guid = tmp_table->guid;
+			table = tmp_table->table;
+		}
+
+		if (!(efi_guidcmp(guid, ACPI_TABLE_GUID)))
+			rsdp_addr = (acpi_physical_address)table;
+		else if (!(efi_guidcmp(guid, ACPI_20_TABLE_GUID)))
+			return (acpi_physical_address)table;
+	}
+	return rsdp_addr;
+#endif
+}
-- 
2.19.2