vmalloc: choose a better start address in vm_area_register_early()

Percpu embedded first chunk allocator is the firstly option, but it
could fail on ARM64, eg,

  percpu: max_distance=0x5fcfdc640000 too large for vmalloc space 0x781fefff0000
  percpu: max_distance=0x600000540000 too large for vmalloc space 0x7dffb7ff0000
  percpu: max_distance=0x5fff9adb0000 too large for vmalloc space 0x5dffb7ff0000

then we could get to

  WARNING: CPU: 15 PID: 461 at vmalloc.c:3087 pcpu_get_vm_areas+0x488/0x838

and the system cannot boot successfully.

Let's implement page mapping percpu first chunk allocator as a fallback
to the embedding allocator to increase the robustness of the system.

Also fix a crash when both NEED_PER_CPU_PAGE_FIRST_CHUNK and
KASAN_VMALLOC enabled.

Tested on ARM64 qemu with cmdline "percpu_alloc=page".

This patch (of 3):

There are some fixed locations in the vmalloc area be reserved in
ARM(see iotable_init()) and ARM64(see map_kernel()), but for
pcpu_page_first_chunk(), it calls vm_area_register_early() and choose
VMALLOC_START as the start address of vmap area which could be
conflicted with above address, then could trigger a BUG_ON in
vm_area_add_early().

Let's choose a suit start address by traversing the vmlist.

Link: https://lkml.kernel.org/r/20210910053354.26721-1-wangkefeng.wang@huawei.com
Link: https://lkml.kernel.org/r/20210910053354.26721-2-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmalloc.c

@@ -2276,15 +2276,21 @@ void __init vm_area_add_early(struct vm_struct *vm)
  */
 void __init vm_area_register_early(struct vm_struct *vm, size_t align)
 {
-	static size_t vm_init_off __initdata;
-	unsigned long addr;
+	unsigned long addr = ALIGN(VMALLOC_START, align);
+	struct vm_struct *cur, **p;
 
-	addr = ALIGN(VMALLOC_START + vm_init_off, align);
-	vm_init_off = PFN_ALIGN(addr + vm->size) - VMALLOC_START;
+	BUG_ON(vmap_initialized);
 
-	vm->addr = (void *)addr;
+	for (p = &vmlist; (cur = *p) != NULL; p = &cur->next) {
+		if ((unsigned long)cur->addr - addr >= vm->size)
+			break;
+		addr = ALIGN((unsigned long)cur->addr + cur->size, align);
+	}
 
-	vm_area_add_early(vm);
+	BUG_ON(addr > VMALLOC_END - vm->size);
+	vm->addr = (void *)addr;
+	vm->next = *p;
+	*p = vm;
 }
 
 static void vmap_init_free_space(void)