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;
 }