vmalloc: implement vm_area_register_early()

Impact: allow multiple early vm areas

There are places where kernel VM area needs to be allocated before
vmalloc is initialized.  This is done by allocating static vm_struct,
initializing several fields and linking it to vmlist and later vmalloc
initialization picking up these from vmlist.  This is currently done
manually and if there's more than one such areas, there's no defined
way to arbitrate who gets which address.

This patch implements vm_area_register_early(), which takes vm_area
struct with flags and size initialized, assigns address to it and puts
it on the vmlist.  This way, multiple early vm areas can determine
which addresses they should use.  The only current user - alpha mm
init - is converted to use it.
Signed-off-by: Tejun Heo <tj@kernel.org>

arch/alpha/mm/init.c

@@ -189,9 +189,21 @@ callback_init(void * kernel_end)
 
 	if (alpha_using_srm) {
 		static struct vm_struct console_remap_vm;
-		unsigned long vaddr = VMALLOC_START;
+		unsigned long nr_pages = 0;
+		unsigned long vaddr;
 		unsigned long i, j;
 
+		/* calculate needed size */
+		for (i = 0; i < crb->map_entries; ++i)
+			nr_pages += crb->map[i].count;
+
+		/* register the vm area */
+		console_remap_vm.flags = VM_ALLOC;
+		console_remap_vm.size = nr_pages << PAGE_SHIFT;
+		vm_area_register_early(&console_remap_vm);
+
+		vaddr = (unsigned long)consle_remap_vm.addr;
+
 		/* Set up the third level PTEs and update the virtual
 		   addresses of the CRB entries.  */
 		for (i = 0; i < crb->map_entries; ++i) {
@@ -213,12 +225,6 @@ callback_init(void * kernel_end)
 				vaddr += PAGE_SIZE;
 			}
 		}
-
-		/* Let vmalloc know that we've allocated some space.  */
-		console_remap_vm.flags = VM_ALLOC;
-		console_remap_vm.addr = (void *) VMALLOC_START;
-		console_remap_vm.size = vaddr - VMALLOC_START;
-		vmlist = &console_remap_vm;
 	}
 
 	callback_init_done = 1;

include/linux/vmalloc.h

@@ -106,5 +106,6 @@ extern long vwrite(char *buf, char *addr, unsigned long count);
  */
 extern rwlock_t vmlist_lock;
 extern struct vm_struct *vmlist;
+extern __init void vm_area_register_early(struct vm_struct *vm);
 
 #endif /* _LINUX_VMALLOC_H */

mm/vmalloc.c

@@ -24,6 +24,7 @@
 #include <linux/radix-tree.h>
 #include <linux/rcupdate.h>
 #include <linux/bootmem.h>
+#include <linux/pfn.h>
 
 #include <asm/atomic.h>
 #include <asm/uaccess.h>
@@ -982,6 +983,29 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node, pgprot_t pro
 }
 EXPORT_SYMBOL(vm_map_ram);
 
+/**
+ * vm_area_register_early - register vmap area early during boot
+ * @vm: vm_struct to register
+ * @size: size of area to register
+ *
+ * This function is used to register kernel vm area before
+ * vmalloc_init() is called.  @vm->size and @vm->flags should contain
+ * proper values on entry and other fields should be zero.  On return,
+ * vm->addr contains the allocated address.
+ *
+ * DO NOT USE THIS FUNCTION UNLESS YOU KNOW WHAT YOU'RE DOING.
+ */
+void __init vm_area_register_early(struct vm_struct *vm)
+{
+	static size_t vm_init_off __initdata;
+
+	vm->addr = (void *)VMALLOC_START + vm_init_off;
+	vm_init_off = PFN_ALIGN(vm_init_off + vm->size);
+
+	vm->next = vmlist;
+	vmlist = vm;
+}
+
 void __init vmalloc_init(void)
 {
 	struct vmap_area *va;