mm: vmalloc: implement vrealloc()

Implement vrealloc() analogous to krealloc().

Currently, krealloc() requires the caller to pass the size of the
previous memory allocation, which, instead, should be self-contained.

We attempt to fix this in a subsequent patch which, in order to do so,
requires vrealloc().

Besides that, we need realloc() functions for kernel allocators in Rust
too. With `Vec` potentially growing (and shrinking) data structures are
rather common.

Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

3 files changed, 79 insertions, 0 deletions

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index e4a631ec430b..ad2ce7a6ab7a 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -189,6 +189,10 @@ extern void *__vcalloc_noprof(size_t n, size_t size, gfp_t flags) __alloc_size(1
 extern void *vcalloc_noprof(size_t n, size_t size) __alloc_size(1, 2);
 #define vcalloc(...)		alloc_hooks(vcalloc_noprof(__VA_ARGS__))
 
+void * __must_check vrealloc_noprof(const void *p, size_t size, gfp_t flags)
+		__realloc_size(2);
+#define vrealloc(...)		alloc_hooks(vrealloc_noprof(__VA_ARGS__))
+
 extern void vfree(const void *addr);
 extern void vfree_atomic(const void *addr);
 
diff --git a/mm/nommu.c b/mm/nommu.c
index 7296e775e04e..40cac1348b40 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -126,6 +126,11 @@ void *__vmalloc_noprof(unsigned long size, gfp_t gfp_mask)
 }
 EXPORT_SYMBOL(__vmalloc_noprof);
 
+void *vrealloc_noprof(const void *p, size_t size, gfp_t flags)
+{
+	return krealloc_noprof(p, size, (flags | __GFP_COMP) & ~__GFP_HIGHMEM);
+}
+
 void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align,
 		unsigned long start, unsigned long end, gfp_t gfp_mask,
 		pgprot_t prot, unsigned long vm_flags, int node,
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 6b783baf12a1..48cc10dd06c0 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4037,6 +4037,76 @@ void *vzalloc_node_noprof(unsigned long size, int node)
 }
 EXPORT_SYMBOL(vzalloc_node_noprof);
 
+/**
+ * vrealloc - reallocate virtually contiguous memory; contents remain unchanged
+ * @p: object to reallocate memory for
+ * @size: the size to reallocate
+ * @flags: the flags for the page level allocator
+ *
+ * If @p is %NULL, vrealloc() behaves exactly like vmalloc(). If @size is 0 and
+ * @p is not a %NULL pointer, the object pointed to is freed.
+ *
+ * If __GFP_ZERO logic is requested, callers must ensure that, starting with the
+ * initial memory allocation, every subsequent call to this API for the same
+ * memory allocation is flagged with __GFP_ZERO. Otherwise, it is possible that
+ * __GFP_ZERO is not fully honored by this API.
+ *
+ * In any case, the contents of the object pointed to are preserved up to the
+ * lesser of the new and old sizes.
+ *
+ * This function must not be called concurrently with itself or vfree() for the
+ * same memory allocation.
+ *
+ * Return: pointer to the allocated memory; %NULL if @size is zero or in case of
+ *         failure
+ */
+void *vrealloc_noprof(const void *p, size_t size, gfp_t flags)
+{
+	size_t old_size = 0;
+	void *n;
+
+	if (!size) {
+		vfree(p);
+		return NULL;
+	}
+
+	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);
+	}
+
+	/*
+	 * TODO: Shrink the vm_area, i.e. unmap and free unused pages. What
+	 * 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))
+			memset((void *)p + size, 0, old_size - size);
+
+		return (void *)p;
+	}
+
+	/* TODO: Grow the vm_area, i.e. allocate and map additional pages. */
+	n = __vmalloc_noprof(size, flags);
+	if (!n)
+		return NULL;
+
+	if (p) {
+		memcpy(n, p, old_size);
+		vfree(p);
+	}
+
+	return n;
+}
+
 #if defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA32)
 #define GFP_VMALLOC32 (GFP_DMA32 | GFP_KERNEL)
 #elif defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA)