efi: add API to reserve memory persistently across kexec reboot

Add kernel plumbing to reserve memory regions persistently on a EFI
system by adding entries to the MEMRESERVE linked list.
Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

drivers/firmware/efi/efi.c

@@ -962,6 +962,38 @@ bool efi_is_table_address(unsigned long phys_addr)
 	return false;
 }
 
+static DEFINE_SPINLOCK(efi_mem_reserve_persistent_lock);
+
+int efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
+{
+	struct linux_efi_memreserve *rsv, *parent;
+
+	if (efi.mem_reserve == EFI_INVALID_TABLE_ADDR)
+		return -ENODEV;
+
+	rsv = kmalloc(sizeof(*rsv), GFP_KERNEL);
+	if (!rsv)
+		return -ENOMEM;
+
+	parent = memremap(efi.mem_reserve, sizeof(*rsv), MEMREMAP_WB);
+	if (!parent) {
+		kfree(rsv);
+		return -ENOMEM;
+	}
+
+	rsv->base = addr;
+	rsv->size = size;
+
+	spin_lock(&efi_mem_reserve_persistent_lock);
+	rsv->next = parent->next;
+	parent->next = __pa(rsv);
+	spin_unlock(&efi_mem_reserve_persistent_lock);
+
+	memunmap(parent);
+
+	return 0;
+}
+
 #ifdef CONFIG_KEXEC
 static int update_efi_random_seed(struct notifier_block *nb,
 				  unsigned long code, void *unused)

include/linux/efi.h

@@ -1043,6 +1043,7 @@ extern int __init efi_uart_console_only (void);
 extern u64 efi_mem_desc_end(efi_memory_desc_t *md);
 extern int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md);
 extern void efi_mem_reserve(phys_addr_t addr, u64 size);
+extern int efi_mem_reserve_persistent(phys_addr_t addr, u64 size);
 extern void efi_initialize_iomem_resources(struct resource *code_resource,
 		struct resource *data_resource, struct resource *bss_resource);
 extern void efi_reserve_boot_services(void);