efi: honour memory reservations passed via a linux specific config table

In order to allow the OS to reserve memory persistently across a
kexec, introduce a Linux-specific UEFI configuration table that
points to the head of a linked list in memory, allowing each kernel
to add list items describing memory regions that the next kernel
should treat as reserved.

This is useful, e.g., for GICv3 based ARM systems that cannot disable
DMA access to the LPI tables, forcing them to reuse the same memory
region again after a kexec reboot.
Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

drivers/firmware/efi/efi.c

@@ -52,7 +52,8 @@ struct efi __read_mostly efi = {
 	.properties_table	= EFI_INVALID_TABLE_ADDR,
 	.mem_attr_table		= EFI_INVALID_TABLE_ADDR,
 	.rng_seed		= EFI_INVALID_TABLE_ADDR,
-	.tpm_log		= EFI_INVALID_TABLE_ADDR
+	.tpm_log		= EFI_INVALID_TABLE_ADDR,
+	.mem_reserve		= EFI_INVALID_TABLE_ADDR,
 };
 EXPORT_SYMBOL(efi);
 
@@ -484,6 +485,7 @@ static __initdata efi_config_table_type_t common_tables[] = {
 	{EFI_MEMORY_ATTRIBUTES_TABLE_GUID, "MEMATTR", &efi.mem_attr_table},
 	{LINUX_EFI_RANDOM_SEED_TABLE_GUID, "RNG", &efi.rng_seed},
 	{LINUX_EFI_TPM_EVENT_LOG_GUID, "TPMEventLog", &efi.tpm_log},
+	{LINUX_EFI_MEMRESERVE_TABLE_GUID, "MEMRESERVE", &efi.mem_reserve},
 	{NULL_GUID, NULL, NULL},
 };
 
@@ -591,6 +593,29 @@ int __init efi_config_parse_tables(void *config_tables, int count, int sz,
 		early_memunmap(tbl, sizeof(*tbl));
 	}
 
+	if (efi.mem_reserve != EFI_INVALID_TABLE_ADDR) {
+		unsigned long prsv = efi.mem_reserve;
+
+		while (prsv) {
+			struct linux_efi_memreserve *rsv;
+
+			/* reserve the entry itself */
+			memblock_reserve(prsv, sizeof(*rsv));
+
+			rsv = early_memremap(prsv, sizeof(*rsv));
+			if (rsv == NULL) {
+				pr_err("Could not map UEFI memreserve entry!\n");
+				return -ENOMEM;
+			}
+
+			if (rsv->size)
+				memblock_reserve(rsv->base, rsv->size);
+
+			prsv = rsv->next;
+			early_memunmap(rsv, sizeof(*rsv));
+		}
+	}
+
 	return 0;
 }
 

include/linux/efi.h

@@ -672,6 +672,7 @@ void efi_native_runtime_setup(void);
 #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)
 #define LINUX_EFI_TPM_EVENT_LOG_GUID		EFI_GUID(0xb7799cb0, 0xeca2, 0x4943,  0x96, 0x67, 0x1f, 0xae, 0x07, 0xb7, 0x47, 0xfa)
+#define LINUX_EFI_MEMRESERVE_TABLE_GUID		EFI_GUID(0x888eb0c6, 0x8ede, 0x4ff5,  0xa8, 0xf0, 0x9a, 0xee, 0x5c, 0xb9, 0x77, 0xc2)
 
 typedef struct {
 	efi_guid_t guid;
@@ -957,6 +958,7 @@ extern struct efi {
 	unsigned long mem_attr_table;	/* memory attributes table */
 	unsigned long rng_seed;		/* UEFI firmware random seed */
 	unsigned long tpm_log;		/* TPM2 Event Log table */
+	unsigned long mem_reserve;	/* Linux EFI memreserve table */
 	efi_get_time_t *get_time;
 	efi_set_time_t *set_time;
 	efi_get_wakeup_time_t *get_wakeup_time;
@@ -1662,4 +1664,10 @@ extern int efi_tpm_eventlog_init(void);
 /* Workqueue to queue EFI Runtime Services */
 extern struct workqueue_struct *efi_rts_wq;
 
+struct linux_efi_memreserve {
+	phys_addr_t	next;
+	phys_addr_t	base;
+	phys_addr_t	size;
+};
+
 #endif /* _LINUX_EFI_H */