mm: vmalloc: Support more granular vrealloc() sizing

index 31e9ffd936e3..5ca8d4dd149d 100644
@@ -61,6 +61,7 @@ struct vm_struct {
 	unsigned int		nr_pages;
 	phys_addr_t		phys_addr;
 	const void		*caller;
+	unsigned long		requested_size;
 };
 
 struct vmap_area {

index 3ed720a787ec..2d7511654831 100644
@@ -1940,7 +1940,7 @@ static inline void setup_vmalloc_vm(struct vm_struct *vm,
 {
 	vm->flags = flags;
 	vm->addr = (void *)va->va_start;
-	vm->size = va_size(va);
+	vm->size = vm->requested_size = va_size(va);
 	vm->caller = caller;
 	va->vm = vm;
 }

@@ -3133,6 +3133,7 @@ struct vm_struct *__get_vm_area_node(unsigned long size,
 
 	area->flags = flags;
 	area->caller = caller;
+	area->requested_size = requested_size;
 
 	va = alloc_vmap_area(size, align, start, end, node, gfp_mask, 0, area);
 	if (IS_ERR(va)) {

@@ -4063,6 +4064,8 @@ EXPORT_SYMBOL(vzalloc_node_noprof);
  */
 void *vrealloc_noprof(const void *p, size_t size, gfp_t flags)
 {
+	struct vm_struct *vm = NULL;
+	size_t alloced_size = 0;
 	size_t old_size = 0;
 	void *n;
 

@@ -4072,15 +4075,17 @@ void *vrealloc_noprof(const void *p, size_t size, gfp_t flags)
 	}
 
 	if (p) {
-		struct vm_struct *vm;
-
 		vm = find_vm_area(p);
 		if (unlikely(!vm)) {
 			WARN(1, "Trying to vrealloc() nonexistent vm area (%p)\n", p);
 			return NULL;
 		}
 
-		old_size = get_vm_area_size(vm);
+		alloced_size = get_vm_area_size(vm);
+		old_size = vm->requested_size;
+		if (WARN(alloced_size < old_size,
+			 "vrealloc() has mismatched area vs requested sizes (%p)\n", p))
+			return NULL;
 	}
 
 	/*

@@ -4088,14 +4093,26 @@ void *vrealloc_noprof(const void *p, size_t size, gfp_t flags)
 	 * would be a good heuristic for when to shrink the vm_area?
 	 */
 	if (size <= old_size) {
-		/* Zero out spare memory. */
-		if (want_init_on_alloc(flags))
+		/* Zero out "freed" memory. */
+		if (want_init_on_free())
 			memset((void *)p + size, 0, old_size - size);
+		vm->requested_size = size;
 		kasan_poison_vmalloc(p + size, old_size - size);
-		kasan_unpoison_vmalloc(p, size, KASAN_VMALLOC_PROT_NORMAL);
 		return (void *)p;
 	}
 
+	/*
+	 * We already have the bytes available in the allocation; use them.
+	 */
+	if (size <= alloced_size) {
+		kasan_unpoison_vmalloc(p + old_size, size - old_size,
+				       KASAN_VMALLOC_PROT_NORMAL);
+		/* Zero out "alloced" memory. */
+		if (want_init_on_alloc(flags))
+			memset((void *)p + old_size, 0, size - old_size);
+		vm->requested_size = size;
+	}
+
 	/* TODO: Grow the vm_area, i.e. allocate and map additional pages. */
 	n = __vmalloc_noprof(size, flags);
 	if (!n)