[PATCH 03/10] mm: add a vmap_pfn function

[Christoph Hellwig <hch@xxxxxx>]

Add a proper helper to remap PFNs into kernel virtual space so that
drivers don't have to abuse alloc_vm_area and open coded PTE
manipulation for it.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 include/linux/vmalloc.h |  1 +
 mm/Kconfig              |  3 +++
 mm/vmalloc.c            | 45 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index b899681e3ff9f0..c77efeac242514 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -122,6 +122,7 @@ extern void vfree_atomic(const void *addr);
 
 extern void *vmap(struct page **pages, unsigned int count,
                        unsigned long flags, pgprot_t prot);
+void *vmap_pfn(unsigned long *pfns, unsigned int count, pgprot_t prot);
 extern void vunmap(const void *addr);
 
 extern int remap_vmalloc_range_partial(struct vm_area_struct *vma,
diff --git a/mm/Kconfig b/mm/Kconfig
index 6c974888f86f97..6fa7ba1199eb1e 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -815,6 +815,9 @@ config DEVICE_PRIVATE
          memory; i.e., memory that is only accessible from the device (or
          group of devices). You likely also want to select HMM_MIRROR.
 
+config VMAP_PFN
+       bool
+
 config FRAME_VECTOR
        bool
 
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ffad65f052c3f9..e2a2ded8d93478 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2413,6 +2413,51 @@ void *vmap(struct page **pages, unsigned int count,
 }
 EXPORT_SYMBOL(vmap);
 
+#ifdef CONFIG_VMAP_PFN
+struct vmap_pfn_data {
+       unsigned long   *pfns;
+       pgprot_t        prot;
+       unsigned int    idx;
+};
+
+static int vmap_pfn_apply(pte_t *pte, unsigned long addr, void *private)
+{
+       struct vmap_pfn_data *data = private;
+
+       if (WARN_ON_ONCE(pfn_valid(data->pfns[data->idx])))
+               return -EINVAL;
+       *pte = pte_mkspecial(pfn_pte(data->pfns[data->idx++], data->prot));
+       return 0;
+}
+
+/**
+ * vmap_pfn - map an array of PFNs into virtually contiguous space
+ * @pfns: array of PFNs
+ * @count: number of pages to map
+ * @prot: page protection for the mapping
+ *
+ * Maps @count PFNs from @pfns into contiguous kernel virtual space and returns
+ * the start address of the mapping.
+ */
+void *vmap_pfn(unsigned long *pfns, unsigned int count, pgprot_t prot)
+{
+       struct vmap_pfn_data data = { .pfns = pfns, .prot = pgprot_nx(prot) };
+       struct vm_struct *area;
+
+       area = get_vm_area_caller(count * PAGE_SIZE, VM_IOREMAP,
+                       __builtin_return_address(0));
+       if (!area)
+               return NULL;
+       if (apply_to_page_range(&init_mm, (unsigned long)area->addr,
+                       count * PAGE_SIZE, vmap_pfn_apply, &data)) {
+               free_vm_area(area);
+               return NULL;
+       }
+       return area->addr;
+}
+EXPORT_SYMBOL_GPL(vmap_pfn);
+#endif /* CONFIG_VMAP_PFN */
+
 static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
                                 pgprot_t prot, int node)
 {
-- 
2.28.0