+/*
+ * Free up the buffer.
+ */
+static void big_key_free_buffer(struct big_key_buf *buf)
+{
+ unsigned int i;
+
+ if (buf->virt) {
+ memset(buf->virt, 0, buf->nr_pages * PAGE_SIZE);
+ vunmap(buf->virt);
+ }
+
+ for (i = 0; i < buf->nr_pages; i++)
+ if (buf->pages[i])
+ __free_page(buf->pages[i]);
+
+ kfree(buf);
+}
+
+/*
+ * Allocate a buffer consisting of a set of pages with a virtual mapping
+ * applied over them.
+ */
+static void *big_key_alloc_buffer(size_t len)
+{
+ struct big_key_buf *buf;
+ unsigned int npg = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ unsigned int i, l;
+
+ buf = kzalloc(sizeof(struct big_key_buf) +
+ sizeof(struct page) * npg +
+ sizeof(struct scatterlist) * npg,
+ GFP_KERNEL);
+ if (!buf)
+ return NULL;
+
+ buf->nr_pages = npg;
+ buf->sg = (void *)(buf->pages + npg);
+ sg_init_table(buf->sg, npg);
+
+ for (i = 0; i < buf->nr_pages; i++) {
+ buf->pages[i] = alloc_page(GFP_KERNEL);
+ if (!buf->pages[i])
+ goto nomem;
+
+ l = min_t(size_t, len, PAGE_SIZE);
+ sg_set_page(&buf->sg[i], buf->pages[i], l, 0);
+ len -= l;
+ }
+
+ buf->virt = vmap(buf->pages, buf->nr_pages, VM_MAP, PAGE_KERNEL);
+ if (!buf->virt)
+ goto nomem;
+
+ return buf;
+
+nomem:
+ big_key_free_buffer(buf);
+ return NULL;
+}
+