mm, powerpc: use vma_kernel_pagesize() in vma_mmu_pagesize()

Patch series "mm, smaps: MMUPageSize for device-dax", v3.

Similar to commit 31383c6865a5 ("mm, hugetlbfs: introduce ->split() to
vm_operations_struct") here is another occasion where we want
special-case hugetlbfs/hstate enabling to also apply to device-dax.

This prompts the question what other hstate conversions we might do
beyond ->split() and ->pagesize(), but this appears to be the last of
the usages of hstate_vma() in generic/non-hugetlbfs specific code paths.

This patch (of 3):

The current powerpc definition of vma_mmu_pagesize() open codes looking
up the page size via hstate.  It is identical to the generic
vma_kernel_pagesize() implementation.

Now, vma_kernel_pagesize() is growing support for determining the page
size of Device-DAX vmas in addition to the existing Hugetlbfs page size
determination.

Ideally, if the powerpc vma_mmu_pagesize() used vma_kernel_pagesize() it
would automatically benefit from any new vma-type support that is added
to vma_kernel_pagesize().  However, the powerpc vma_mmu_pagesize() is
prevented from calling vma_kernel_pagesize() due to a circular header
dependency that requires vma_mmu_pagesize() to be defined before
including <linux/hugetlb.h>.

Break this circular dependency by defining the default vma_mmu_pagesize()
as a __weak symbol to be overridden by the powerpc version.

Link: http://lkml.kernel.org/r/151996254179.27922.2213728278535578744.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Jane Chu <jane.chu@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/include/asm/hugetlb.h

@@ -117,12 +117,6 @@ void hugetlb_free_pgd_range(struct mmu_gather *tlb, unsigned long addr,
 			    unsigned long end, unsigned long floor,
 			    unsigned long ceiling);
 
-/*
- * The version of vma_mmu_pagesize() in arch/powerpc/mm/hugetlbpage.c needs
- * to override the version in mm/hugetlb.c
- */
-#define vma_mmu_pagesize vma_mmu_pagesize
-
 /*
  * If the arch doesn't supply something else, assume that hugepage
  * size aligned regions are ok without further preparation.

arch/powerpc/mm/hugetlbpage.c

@@ -568,10 +568,7 @@ unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
 	if (!radix_enabled())
 		return 1UL << mmu_psize_to_shift(psize);
 #endif
-	if (!is_vm_hugetlb_page(vma))
-		return PAGE_SIZE;
-
-	return huge_page_size(hstate_vma(vma));
+	return vma_kernel_pagesize(vma);
 }
 
 static inline bool is_power_of_4(unsigned long x)

mm/hugetlb.c

@@ -651,15 +651,13 @@ EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
 /*
  * Return the page size being used by the MMU to back a VMA. In the majority
  * of cases, the page size used by the kernel matches the MMU size. On
- * architectures where it differs, an architecture-specific version of this
- * function is required.
+ * architectures where it differs, an architecture-specific 'strong'
+ * version of this symbol is required.
  */
-#ifndef vma_mmu_pagesize
-unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
+__weak unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
 {
 	return vma_kernel_pagesize(vma);
 }
-#endif
 
 /*
  * Flags for MAP_PRIVATE reservations.  These are stored in the bottom