Commit 121e6f3258fe3 ("mm/vmalloc: hugepage vmalloc mappings") added
support for hugepage vmalloc mappings, it also added the flag
VM_NO_HUGE_VMAP for __vmalloc_node_range to request the allocation to
be performed with 0-order non-huge pages.  This flag is not accessible
when calling vmalloc, the only option is to call directly
__vmalloc_node_range, which is not exported.

This means that a module can't vmalloc memory with small pages.

Case in point: KVM on s390x needs to vmalloc a large area, and it needs
to be mapped with non-huge pages, because of a hardware limitation.

This patch adds the function vmalloc_no_huge, which works like vmalloc,
but it is guaranteed to always back the mapping using small pages. This
new function is exported, therefore it is usable by modules.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Thomas Gleixner <redacted>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Christoph Hellwig <hch@infradead.org>
---
  include/linux/vmalloc.h |  1 +
  mm/vmalloc.c            | 16 ++++++++++++++++
  2 files changed, 17 insertions(+)

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 4d668abb6391..bfaaf0b6fa76 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h

@@ -135,6 +135,7 @@ extern void *__vmalloc_node_range(unsigned long size, unsigned long align,
  			const void *caller);
  void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask,
  		int node, const void *caller);
+void *vmalloc_no_huge(unsigned long size);
  
  extern void vfree(const void *addr);
  extern void vfree_atomic(const void *addr);

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a13ac524f6ff..296a2fcc3fbe 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c

@@ -2998,6 +2998,22 @@ void *vmalloc(unsigned long size)
  }
  EXPORT_SYMBOL(vmalloc);
  
+/**
+ * vmalloc_no_huge - allocate virtually contiguous memory using small pages
+ * @size:    allocation size
+ *
+ * Allocate enough non-huge pages to cover @size from the page level
+ * allocator and map them into contiguous kernel virtual space.
+ *
+ * Return: pointer to the allocated memory or %NULL on error
+ */
+void *vmalloc_no_huge(unsigned long size)
+{
+	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END, GFP_KERNEL, PAGE_KERNEL,
+				    VM_NO_HUGE_VMAP, NUMA_NO_NODE, __builtin_return_address(0));
+}
+EXPORT_SYMBOL(vmalloc_no_huge);
+
  /**
   * vzalloc - allocate virtually contiguous memory with zero fill
   * @size:    allocation size