efi: libstub: Move screen_info handling to common code

Currently, arm64, RISC-V and LoongArch rely on the fact that struct
screen_info can be accessed directly, due to the fact that the EFI stub
and the core kernel are part of the same image. This will change after a
future patch, so let's ensure that the screen_info handling is able to
deal with this, by adopting the arm32 approach of passing it as a
configuration table. While at it, switch to ACPI reclaim memory to hold
the screen_info data, which is more appropriate for this kind of
allocation.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/arm/include/asm/efi.h

@@ -43,9 +43,6 @@ void efi_virtmap_unload(void);
 
 /* arch specific definitions used by the stub code */
 
-struct screen_info *alloc_screen_info(void);
-void free_screen_info(struct screen_info *si);
-
 /*
  * A reasonable upper bound for the uncompressed kernel size is 32 MBytes,
  * so we will reserve that amount of memory. We have no easy way to tell what

arch/arm/kernel/efi.c

@@ -75,38 +75,13 @@ int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md)
 	return 0;
 }
 
-static unsigned long __initdata screen_info_table = EFI_INVALID_TABLE_ADDR;
 static unsigned long __initdata cpu_state_table = EFI_INVALID_TABLE_ADDR;
 
 const efi_config_table_type_t efi_arch_tables[] __initconst = {
-	{LINUX_EFI_ARM_SCREEN_INFO_TABLE_GUID, &screen_info_table},
 	{LINUX_EFI_ARM_CPU_STATE_TABLE_GUID, &cpu_state_table},
 	{}
 };
 
-static void __init load_screen_info_table(void)
-{
-	struct screen_info *si;
-
-	if (screen_info_table != EFI_INVALID_TABLE_ADDR) {
-		si = early_memremap_ro(screen_info_table, sizeof(*si));
-		if (!si) {
-			pr_err("Could not map screen_info config table\n");
-			return;
-		}
-		screen_info = *si;
-		early_memunmap(si, sizeof(*si));
-
-		/* dummycon on ARM needs non-zero values for columns/lines */
-		screen_info.orig_video_cols = 80;
-		screen_info.orig_video_lines = 25;
-
-		if (memblock_is_map_memory(screen_info.lfb_base))
-			memblock_mark_nomap(screen_info.lfb_base,
-					    screen_info.lfb_size);
-	}
-}
-
 static void __init load_cpu_state_table(void)
 {
 	if (cpu_state_table != EFI_INVALID_TABLE_ADDR) {
@@ -145,7 +120,11 @@ void __init arm_efi_init(void)
 {
 	efi_init();
 
-	load_screen_info_table();
+	if (screen_info.orig_video_isVGA == VIDEO_TYPE_EFI) {
+		/* dummycon on ARM needs non-zero values for columns/lines */
+		screen_info.orig_video_cols = 80;
+		screen_info.orig_video_lines = 25;
+	}
 
 	/* ARM does not permit early mappings to persist across paging_init() */
 	efi_memmap_unmap();

arch/arm64/include/asm/efi.h

@@ -84,12 +84,6 @@ static inline unsigned long efi_get_max_initrd_addr(unsigned long image_addr)
 	return (image_addr & ~(SZ_1G - 1UL)) + (1UL << (VA_BITS_MIN - 1));
 }
 
-#define alloc_screen_info(x...)		&screen_info
-
-static inline void free_screen_info(struct screen_info *si)
-{
-}
-
 #define EFI_ALLOC_ALIGN		SZ_64K
 
 /*

arch/loongarch/include/asm/efi.h

@@ -19,15 +19,6 @@ void efifb_setup_from_dmi(struct screen_info *si, const char *opt);
 #define EFI_ALLOC_ALIGN		SZ_64K
 #define EFI_RT_VIRTUAL_OFFSET	CSR_DMW0_BASE
 
-static inline struct screen_info *alloc_screen_info(void)
-{
-	return &screen_info;
-}
-
-static inline void free_screen_info(struct screen_info *si)
-{
-}
-
 static inline unsigned long efi_get_max_initrd_addr(unsigned long image_addr)
 {
 	return ULONG_MAX;

arch/loongarch/kernel/efi.c

@@ -52,6 +52,27 @@ void __init efi_runtime_init(void)
 	set_bit(EFI_RUNTIME_SERVICES, &efi.flags);
 }
 
+unsigned long __initdata screen_info_table = EFI_INVALID_TABLE_ADDR;
+
+static void __init init_screen_info(void)
+{
+	struct screen_info *si;
+
+	if (screen_info_table == EFI_INVALID_TABLE_ADDR)
+		return;
+
+	si = early_memremap(screen_info_table, sizeof(*si));
+	if (!si) {
+		pr_err("Could not map screen_info config table\n");
+		return;
+	}
+	screen_info = *si;
+	memset(si, 0, sizeof(*si));
+	early_memunmap(si, sizeof(*si));
+
+	memblock_reserve(screen_info.lfb_base, screen_info.lfb_size);
+}
+
 void __init efi_init(void)
 {
 	int size;
@@ -80,8 +101,7 @@ void __init efi_init(void)
 
 	set_bit(EFI_CONFIG_TABLES, &efi.flags);
 
-	if (screen_info.orig_video_isVGA == VIDEO_TYPE_EFI)
-		memblock_reserve(screen_info.lfb_base, screen_info.lfb_size);
+	init_screen_info();
 
 	if (boot_memmap == EFI_INVALID_TABLE_ADDR)
 		return;

arch/riscv/include/asm/efi.h

@@ -31,12 +31,6 @@ static inline unsigned long efi_get_max_initrd_addr(unsigned long image_addr)
 	return ULONG_MAX;
 }
 
-#define alloc_screen_info(x...)		(&screen_info)
-
-static inline void free_screen_info(struct screen_info *si)
-{
-}
-
 void efi_virtmap_load(void);
 void efi_virtmap_unload(void);
 

drivers/firmware/efi/efi-init.c

@@ -22,6 +22,8 @@
 
 #include <asm/efi.h>
 
+unsigned long __initdata screen_info_table = EFI_INVALID_TABLE_ADDR;
+
 static int __init is_memory(efi_memory_desc_t *md)
 {
 	if (md->attribute & (EFI_MEMORY_WB|EFI_MEMORY_WT|EFI_MEMORY_WC))
@@ -55,9 +57,22 @@ extern __weak const efi_config_table_type_t efi_arch_tables[];
 
 static void __init init_screen_info(void)
 {
-	if (screen_info.orig_video_isVGA == VIDEO_TYPE_EFI &&
-	    memblock_is_map_memory(screen_info.lfb_base))
-		memblock_mark_nomap(screen_info.lfb_base, screen_info.lfb_size);
+	struct screen_info *si;
+
+	if (screen_info_table != EFI_INVALID_TABLE_ADDR) {
+		si = early_memremap(screen_info_table, sizeof(*si));
+		if (!si) {
+			pr_err("Could not map screen_info config table\n");
+			return;
+		}
+		screen_info = *si;
+		memset(si, 0, sizeof(*si));
+		early_memunmap(si, sizeof(*si));
+
+		if (memblock_is_map_memory(screen_info.lfb_base))
+			memblock_mark_nomap(screen_info.lfb_base,
+					    screen_info.lfb_size);
+	}
 }
 
 static int __init uefi_init(u64 efi_system_table)

drivers/firmware/efi/efi.c

@@ -58,6 +58,8 @@ static unsigned long __initdata mem_reserve = EFI_INVALID_TABLE_ADDR;
 static unsigned long __initdata rt_prop = EFI_INVALID_TABLE_ADDR;
 static unsigned long __initdata initrd = EFI_INVALID_TABLE_ADDR;
 
+extern unsigned long screen_info_table;
+
 struct mm_struct efi_mm = {
 	.mm_mt			= MTREE_INIT_EXT(mm_mt, MM_MT_FLAGS, efi_mm.mmap_lock),
 	.mm_users		= ATOMIC_INIT(2),
@@ -546,6 +548,9 @@ static const efi_config_table_type_t common_tables[] __initconst = {
 #endif
 #ifdef CONFIG_EFI_COCO_SECRET
 	{LINUX_EFI_COCO_SECRET_AREA_GUID,	&efi.coco_secret,	"CocoSecret"	},
+#endif
+#ifdef CONFIG_EFI_GENERIC_STUB
+	{LINUX_EFI_SCREEN_INFO_TABLE_GUID,	&screen_info_table			},
 #endif
 	{},
 };

drivers/firmware/efi/libstub/Makefile

@@ -81,7 +81,8 @@ lib-$(CONFIG_EFI_PARAMS_FROM_FDT) += fdt.o \
 $(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
 	$(call if_changed_rule,cc_o_c)
 
-lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o string.o intrinsics.o systable.o
+lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o string.o intrinsics.o systable.o \
+				   screen_info.o
 
 lib-$(CONFIG_ARM)		+= arm32-stub.o
 lib-$(CONFIG_ARM64)		+= arm64-stub.o arm64-entry.o

drivers/firmware/efi/libstub/arm32-stub.c

@@ -76,43 +76,6 @@ void efi_handle_post_ebs_state(void)
 		      &efi_entry_state->sctlr_after_ebs);
 }
 
-static efi_guid_t screen_info_guid = LINUX_EFI_ARM_SCREEN_INFO_TABLE_GUID;
-
-struct screen_info *alloc_screen_info(void)
-{
-	struct screen_info *si;
-	efi_status_t status;
-
-	/*
-	 * Unlike on arm64, where we can directly fill out the screen_info
-	 * structure from the stub, we need to allocate a buffer to hold
-	 * its contents while we hand over to the kernel proper from the
-	 * decompressor.
-	 */
-	status = efi_bs_call(allocate_pool, EFI_RUNTIME_SERVICES_DATA,
-			     sizeof(*si), (void **)&si);
-
-	if (status != EFI_SUCCESS)
-		return NULL;
-
-	status = efi_bs_call(install_configuration_table,
-			     &screen_info_guid, si);
-	if (status == EFI_SUCCESS)
-		return si;
-
-	efi_bs_call(free_pool, si);
-	return NULL;
-}
-
-void free_screen_info(struct screen_info *si)
-{
-	if (!si)
-		return;
-
-	efi_bs_call(install_configuration_table, &screen_info_guid, NULL);
-	efi_bs_call(free_pool, si);
-}
-
 efi_status_t handle_kernel_image(unsigned long *image_addr,
 				 unsigned long *image_size,
 				 unsigned long *reserve_addr,

drivers/firmware/efi/libstub/efi-stub.c

@@ -47,6 +47,15 @@
 static u64 virtmap_base = EFI_RT_VIRTUAL_BASE;
 static bool flat_va_mapping = (EFI_RT_VIRTUAL_OFFSET != 0);
 
+struct screen_info * __weak alloc_screen_info(void)
+{
+	return &screen_info;
+}
+
+void __weak free_screen_info(struct screen_info *si)
+{
+}
+
 static struct screen_info *setup_graphics(void)
 {
 	efi_guid_t gop_proto = EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID;

drivers/firmware/efi/libstub/efistub.h

@@ -975,4 +975,7 @@ efi_enable_reset_attack_mitigation(void) { }
 
 void efi_retrieve_tpm2_eventlog(void);
 
+struct screen_info *alloc_screen_info(void);
+void free_screen_info(struct screen_info *si);
+
 #endif

drivers/firmware/efi/libstub/screen_info.c

+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/efi.h>
+#include <asm/efi.h>
+
+#include "efistub.h"
+
+/*
+ * There are two ways of populating the core kernel's struct screen_info via the stub:
+ * - using a configuration table, like below, which relies on the EFI init code
+ *   to locate the table and copy the contents;
+ * - by linking directly to the core kernel's copy of the global symbol.
+ *
+ * The latter is preferred because it makes the EFIFB earlycon available very
+ * early, but it only works if the EFI stub is part of the core kernel image
+ * itself. The zboot decompressor can only use the configuration table
+ * approach.
+ *
+ * In order to support both methods from the same build of the EFI stub
+ * library, provide this dummy global definition of struct screen_info. If it
+ * is required to satisfy a link dependency, it means we need to override the
+ * __weak alloc and free methods with the ones below, and those will be pulled
+ * in as well.
+ */
+struct screen_info screen_info;
+
+static efi_guid_t screen_info_guid = LINUX_EFI_SCREEN_INFO_TABLE_GUID;
+
+struct screen_info *alloc_screen_info(void)
+{
+	struct screen_info *si;
+	efi_status_t status;
+
+	status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
+			     sizeof(*si), (void **)&si);
+
+	if (status != EFI_SUCCESS)
+		return NULL;
+
+	status = efi_bs_call(install_configuration_table,
+			     &screen_info_guid, si);
+	if (status == EFI_SUCCESS)
+		return si;
+
+	efi_bs_call(free_pool, si);
+	return NULL;
+}
+
+void free_screen_info(struct screen_info *si)
+{
+	if (!si)
+		return;
+
+	efi_bs_call(install_configuration_table, &screen_info_guid, NULL);
+	efi_bs_call(free_pool, si);
+}

include/linux/efi.h

@@ -403,7 +403,7 @@ void efi_native_runtime_setup(void);
  * structure that was populated by the stub based on the GOP protocol instance
  * associated with ConOut
  */
-#define LINUX_EFI_ARM_SCREEN_INFO_TABLE_GUID	EFI_GUID(0xe03fc20a, 0x85dc, 0x406e,  0xb9, 0x0e, 0x4a, 0xb5, 0x02, 0x37, 0x1d, 0x95)
+#define LINUX_EFI_SCREEN_INFO_TABLE_GUID	EFI_GUID(0xe03fc20a, 0x85dc, 0x406e,  0xb9, 0x0e, 0x4a, 0xb5, 0x02, 0x37, 0x1d, 0x95)
 #define LINUX_EFI_ARM_CPU_STATE_TABLE_GUID	EFI_GUID(0xef79e4aa, 0x3c3d, 0x4989,  0xb9, 0x02, 0x07, 0xa9, 0x43, 0xe5, 0x50, 0xd2)
 #define LINUX_EFI_LOADER_ENTRY_GUID		EFI_GUID(0x4a67b082, 0x0a4c, 0x41cf,  0xb6, 0xc7, 0x44, 0x0b, 0x29, 0xbb, 0x8c, 0x4f)
 #define LINUX_EFI_RANDOM_SEED_TABLE_GUID	EFI_GUID(0x1ce1e5bc, 0x7ceb, 0x42f2,  0x81, 0xe5, 0x8a, 0xad, 0xf1, 0x80, 0xf5, 0x7b)