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Subject[PATCH v7 29/45] x86/compressed/acpi: move EFI system table lookup to helper
Date
From: Michael Roth <michael.roth@amd.com>

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>
---
arch/x86/boot/compressed/Makefile | 1 +
arch/x86/boot/compressed/acpi.c | 60 ++++++++++----------------
arch/x86/boot/compressed/efi.c | 71 +++++++++++++++++++++++++++++++
arch/x86/boot/compressed/misc.h | 14 ++++++
4 files changed, 108 insertions(+), 38 deletions(-)
create mode 100644 arch/x86/boot/compressed/efi.c

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 431bf7f846c3..d364192c2367 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -100,6 +100,7 @@ endif
vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o

vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
+vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
efi-obj-$(CONFIG_EFI_STUB) = $(objtree)/drivers/firmware/efi/libstub/lib.a

$(obj)/vmlinux: $(vmlinux-objs-y) $(efi-obj-y) FORCE
diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
index 8bcbcee54aa1..9e784bd7b2e6 100644
--- a/arch/x86/boot/compressed/acpi.c
+++ b/arch/x86/boot/compressed/acpi.c
@@ -86,8 +86,8 @@ static acpi_physical_address kexec_get_rsdp_addr(void)
{
efi_system_table_64_t *systab;
struct efi_setup_data *esd;
- struct efi_info *ei;
- char *sig;
+ bool efi_64;
+ int ret;

esd = (struct efi_setup_data *)get_kexec_setup_data_addr();
if (!esd)
@@ -98,18 +98,16 @@ static acpi_physical_address kexec_get_rsdp_addr(void)
return 0;
}

- ei = &boot_params->efi_info;
- sig = (char *)&ei->efi_loader_signature;
- if (strncmp(sig, EFI64_LOADER_SIGNATURE, 4)) {
+ /* Get systab from boot params. */
+ ret = efi_get_system_table(boot_params, (unsigned long *)&systab, &efi_64);
+ if (ret)
+ error("EFI system table not found in kexec boot_params.");
+
+ if (!efi_64) {
debug_putstr("Wrong kexec EFI loader signature.\n");
return 0;
}

- /* Get systab from boot params. */
- systab = (efi_system_table_64_t *) (ei->efi_systab | ((__u64)ei->efi_systab_hi << 32));
- if (!systab)
- error("EFI system table not found in kexec boot_params.");
-
return __efi_get_rsdp_addr((unsigned long)esd->tables, systab->nr_tables, true);
}
#else
@@ -119,45 +117,31 @@ 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_tbl_pa, config_tables;
unsigned int nr_tables;
- struct efi_info *ei;
bool efi_64;
- char *sig;
-
- ei = &boot_params->efi_info;
- sig = (char *)&ei->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;
- }
+ int ret;

- /* Get systab from boot params. */
-#ifdef CONFIG_X86_64
- systab = ei->efi_systab | ((__u64)ei->efi_systab_hi << 32);
-#else
- if (ei->efi_systab_hi || ei->efi_memmap_hi) {
- debug_putstr("Error getting RSDP address: EFI system table located above 4GB.\n");
+ /*
+ * This function is called even for non-EFI BIOSes, and callers expect
+ * failure to locate the EFI system table to result in 0 being returned
+ * as indication that EFI is not available, rather than outright
+ * failure/abort.
+ */
+ ret = efi_get_system_table(boot_params, &systab_tbl_pa, &efi_64);
+ if (ret == -EOPNOTSUPP)
return 0;
- }
- systab = ei->efi_systab;
-#endif
- if (!systab)
- error("EFI system table not found.");
+ if (ret)
+ 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_tbl_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_tbl_pa;

config_tables = stbl->tables;
nr_tables = stbl->nr_tables;
diff --git a/arch/x86/boot/compressed/efi.c b/arch/x86/boot/compressed/efi.c
new file mode 100644
index 000000000000..bcf1d5650e26
--- /dev/null
+++ b/arch/x86/boot/compressed/efi.c
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Helpers for early access to EFI configuration table
+ *
+ * Copyright (C) 2021 Advanced Micro Devices, Inc.
+ *
+ * Author: Michael Roth <michael.roth@amd.com>
+ */
+
+#include "misc.h"
+#include <linux/efi.h>
+#include <asm/efi.h>
+
+/**
+ * Given boot_params, retrieve the physical address of EFI system table.
+ *
+ * @boot_params: pointer to boot_params
+ * @sys_tbl_pa: location to store physical address of system table
+ * @is_efi_64: location to store whether using 64-bit EFI or not
+ *
+ * Returns 0 on success. On error, return params are left unchanged.
+ *
+ * Note: Existing callers like ACPI will call this unconditionally even for
+ * non-EFI BIOSes. In such cases, those callers may treat cases where
+ * bootparams doesn't indicate that a valid EFI system table is available as
+ * non-fatal errors to allow fall-through to non-EFI alternatives. This
+ * class of errors are reported as EOPNOTSUPP and should be kept in sync with
+ * callers who check for that specific error.
+ */
+int efi_get_system_table(struct boot_params *boot_params, unsigned long *sys_tbl_pa,
+ bool *is_efi_64)
+{
+ unsigned long sys_tbl;
+ struct efi_info *ei;
+ bool efi_64;
+ char *sig;
+
+ if (!sys_tbl_pa || !is_efi_64)
+ return -EINVAL;
+
+ ei = &boot_params->efi_info;
+ sig = (char *)&ei->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 -EOPNOTSUPP;
+ }
+
+ /* Get systab from boot params. */
+#ifdef CONFIG_X86_64
+ sys_tbl = ei->efi_systab | ((__u64)ei->efi_systab_hi << 32);
+#else
+ if (ei->efi_systab_hi || ei->efi_memmap_hi) {
+ debug_putstr("Error: EFI system table located above 4GB.\n");
+ return -EOPNOTSUPP;
+ }
+ sys_tbl = ei->efi_systab;
+#endif
+ if (!sys_tbl) {
+ debug_putstr("EFI system table not found.");
+ return -ENOENT;
+ }
+
+ *sys_tbl_pa = sys_tbl;
+ *is_efi_64 = efi_64;
+ return 0;
+}
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 01cc13c12059..165640f64b71 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -23,6 +23,7 @@
#include <linux/screen_info.h>
#include <linux/elf.h>
#include <linux/io.h>
+#include <linux/efi.h>
#include <asm/page.h>
#include <asm/boot.h>
#include <asm/bootparam.h>
@@ -176,4 +177,17 @@ void boot_stage2_vc(void);

unsigned long sev_verify_cbit(unsigned long cr3);

+#ifdef CONFIG_EFI
+/* helpers for early EFI config table access */
+int efi_get_system_table(struct boot_params *boot_params,
+ unsigned long *sys_tbl_pa, bool *is_efi_64);
+#else
+static inline int
+efi_get_system_table(struct boot_params *boot_params,
+ unsigned long *sys_tbl_pa, bool *is_efi_64)
+{
+ return -ENOENT;
+}
+#endif /* CONFIG_EFI */
+
#endif /* BOOT_COMPRESSED_MISC_H */
--
2.25.1
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