coreboot exposes (S)MM related data in the coreboot table. Extends existing interface
with structure corresponding to (S)MM data, and adds COREBOOT_PAYLOAD_MM config used by
follow-up patches.

Signed-off-by: Michal Gorlas <michal.gorlas@9elements.com>
---
 drivers/firmware/google/Kconfig          | 12 +++++++
 drivers/firmware/google/coreboot_table.h | 11 ++++++
 drivers/firmware/google/mm_payload.h     | 58 ++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+)

diff --git a/drivers/firmware/google/Kconfig b/drivers/firmware/google/Kconfig
index 41b78f5cb7351e512cbaeb6443634a4b97bf6255..ff443f0c4a9a990052d83903fb0f0b0795cc76bd 100644
--- a/drivers/firmware/google/Kconfig
+++ b/drivers/firmware/google/Kconfig
@@ -81,4 +81,16 @@ config GOOGLE_VPD
 	  This option enables the kernel to expose the content of Google VPD
 	  under /sys/firmware/vpd.
 
+config COREBOOT_PAYLOAD_MM
+	tristate "SMI handling in Linux (LinuxBootSMM)"
+	depends on X86 && GOOGLE_COREBOOT_TABLE
+	help
+	  Enables support for SMI handling by Linux-owned code.
+	  coreboot reserves region for payload-owned SMI handler, the Linux
+	  driver prepares its SMI handler outside of SMRAM, and lets coreboot
+	  know where the handler is placed by issuing an SMI. On this SMI, the
+	  handler is being placed in SMRAM and all supported SMIs from that point
+	  on are handled by Linux-owned SMI handler.
+	  If in doubt, say N.
+
 endif # GOOGLE_FIRMWARE
diff --git a/drivers/firmware/google/coreboot_table.h b/drivers/firmware/google/coreboot_table.h
index bb6f0f7299b4670d0b1f91bd7a3c038cdb412f7b..8a7934e679903e39ce1d86b4aecbc2b4e89363fd 100644
--- a/drivers/firmware/google/coreboot_table.h
+++ b/drivers/firmware/google/coreboot_table.h
@@ -52,6 +52,16 @@ struct lb_cbmem_entry {
 	u32 id;
 };
 
+/* Corresponds to LB_TAG_PLD_MM_INTERFACE_INFO */
+#define LB_TAG_PLD_MM_INTERFACE_INFO 0x3b
+struct lb_pld_mm_interface_info {
+	u32 tag;
+	u32 size;
+	u8 revision;
+	u8 requires_long_mode_call;
+	u8 register_mm_entry_command;
+};
+
 /* Describes framebuffer setup by coreboot */
 struct lb_framebuffer {
 	u32 tag;
@@ -80,6 +90,7 @@ struct coreboot_device {
 		struct lb_cbmem_ref cbmem_ref;
 		struct lb_cbmem_entry cbmem_entry;
 		struct lb_framebuffer framebuffer;
+		struct lb_pld_mm_interface_info mm_info;
 		DECLARE_FLEX_ARRAY(u8, raw);
 	};
 };
diff --git a/drivers/firmware/google/mm_payload.h b/drivers/firmware/google/mm_payload.h
new file mode 100644
index 0000000000000000000000000000000000000000..bb2f55c4f24096dfd526e281a937f100031d5315
--- /dev/null
+++ b/drivers/firmware/google/mm_payload.h
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * mm_payload.h
+ *
+ * Internal header for MM payload driver.
+ *
+ * Copyright 2025 9elements gmbh
+ * Copyright 2025 Michal Gorlas <michal.gorlas@9elements.com>
+ */
+
+#ifndef __MM_PAYLOAD_H
+#define __MM_PAYLOAD_H
+
+#define PAYLOAD_MM_RET_SUCCESS 0
+#define PAYLOAD_MM_RET_FAILURE 1
+#define PAYLOAD_MM_REGISTER_ENTRY 2
+
+#define REALMODE_END_SIGNATURE	0x65a22c82
+
+struct mm_info {
+	u8 revision;
+	u8 requires_long_mode_call;
+	u8 register_mm_entry_command;
+};
+
+extern struct mm_info *mm_info;
+
+#ifndef __ASSEMBLY__
+
+#include <linux/types.h>
+
+/* This must match data at mm_handler/mm_header.S */
+struct mm_header {
+	u32	text_start;
+	u32	mm_entry_32;
+	u32	mm_entry_64;
+	u32	mm_signature;
+	u32	mm_blob_size;
+};
+
+extern struct mm_header *mm_header;
+extern unsigned char mm_blob_end[];
+
+extern unsigned char mm_blob[];
+extern unsigned char mm_relocs[];
+
+/*
+ * This has to be under 1MB (see tseg_region.c in coreboot source tree).
+ * The actual check for this is made in coreboot after we fill the header
+ * (see above) with the blob size.
+ */
+static inline size_t mm_payload_size_needed(void)
+{
+	return mm_blob_end - mm_blob;
+}
+
+#endif /* __ASSEMBLER__ */
+#endif /* __MM_PAYLOAD_H */

-- 
2.49.0

On Mon, Jun 16, 2025 at 04:01:12PM +0200, Michal Gorlas wrote:
> coreboot exposes (S)MM related data in the coreboot table. Extends existing interface
> with structure corresponding to (S)MM data, and adds COREBOOT_PAYLOAD_MM config used by
> follow-up patches.

s/Extends/Extend/;s/adds/add/ not a hard requirement but [1]("imperative mood").

It'd be better to annotate what MM and SMM stand for as well.

Symbols introduced in the patch are used in the following patch of the series.
How about just merge them into one patch?

[1]: https://www.kernel.org/doc/html/latest/process/submitting-patches.html