mm/hmm: do not differentiate between empty entry or missing directory

There is no point in differentiating between a range for which there is
not even a directory (and thus entries) and empty entry (pte_none() or
pmd_none() returns true).

Simply drop the distinction ie remove HMM_PFN_EMPTY flag and merge now
duplicate hmm_vma_walk_hole() and hmm_vma_walk_clear() functions.

Link: http://lkml.kernel.org/r/20180323005527.758-11-jglisse@redhat.com
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Evgeny Baskakov <ebaskakov@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mark Hairgrove <mhairgrove@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/hmm.h

@@ -84,7 +84,6 @@ struct hmm;
  * HMM_PFN_VALID: pfn is valid. It has, at least, read permission.
  * HMM_PFN_WRITE: CPU page table has write permission set
  * HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory
- * HMM_PFN_EMPTY: corresponding CPU page table entry is pte_none()
  * HMM_PFN_SPECIAL: corresponding CPU page table entry is special; i.e., the
  *      result of vm_insert_pfn() or vm_insert_page(). Therefore, it should not
  *      be mirrored by a device, because the entry will never have HMM_PFN_VALID
@@ -94,10 +93,9 @@ struct hmm;
 #define HMM_PFN_VALID (1 << 0)
 #define HMM_PFN_WRITE (1 << 1)
 #define HMM_PFN_ERROR (1 << 2)
-#define HMM_PFN_EMPTY (1 << 3)
-#define HMM_PFN_SPECIAL (1 << 4)
-#define HMM_PFN_DEVICE_UNADDRESSABLE (1 << 5)
-#define HMM_PFN_SHIFT 6
+#define HMM_PFN_SPECIAL (1 << 3)
+#define HMM_PFN_DEVICE_UNADDRESSABLE (1 << 4)
+#define HMM_PFN_SHIFT 5
 
 /*
  * hmm_pfn_to_page() - return struct page pointed to by a valid HMM pfn

mm/hmm.c

@@ -348,6 +348,16 @@ static void hmm_pfns_clear(uint64_t *pfns,
 		*pfns = 0;
 }
 
+/*
+ * hmm_vma_walk_hole() - handle a range lacking valid pmd or pte(s)
+ * @start: range virtual start address (inclusive)
+ * @end: range virtual end address (exclusive)
+ * @walk: mm_walk structure
+ * Returns: 0 on success, -EAGAIN after page fault, or page fault error
+ *
+ * This function will be called whenever pmd_none() or pte_none() returns true,
+ * or whenever there is no page directory covering the virtual address range.
+ */
 static int hmm_vma_walk_hole(unsigned long addr,
 			     unsigned long end,
 			     struct mm_walk *walk)
@@ -357,31 +367,6 @@ static int hmm_vma_walk_hole(unsigned long addr,
 	uint64_t *pfns = range->pfns;
 	unsigned long i;
 
-	hmm_vma_walk->last = addr;
-	i = (addr - range->start) >> PAGE_SHIFT;
-	for (; addr < end; addr += PAGE_SIZE, i++) {
-		pfns[i] = HMM_PFN_EMPTY;
-		if (hmm_vma_walk->fault) {
-			int ret;
-
-			ret = hmm_vma_do_fault(walk, addr, &pfns[i]);
-			if (ret != -EAGAIN)
-				return ret;
-		}
-	}
-
-	return hmm_vma_walk->fault ? -EAGAIN : 0;
-}
-
-static int hmm_vma_walk_clear(unsigned long addr,
-			      unsigned long end,
-			      struct mm_walk *walk)
-{
-	struct hmm_vma_walk *hmm_vma_walk = walk->private;
-	struct hmm_range *range = hmm_vma_walk->range;
-	uint64_t *pfns = range->pfns;
-	unsigned long i;
-
 	hmm_vma_walk->last = addr;
 	i = (addr - range->start) >> PAGE_SHIFT;
 	for (; addr < end; addr += PAGE_SIZE, i++) {
@@ -440,10 +425,10 @@ again:
 		if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
 			goto again;
 		if (pmd_protnone(pmd))
-			return hmm_vma_walk_clear(start, end, walk);
+			return hmm_vma_walk_hole(start, end, walk);
 
 		if (write_fault && !pmd_write(pmd))
-			return hmm_vma_walk_clear(start, end, walk);
+			return hmm_vma_walk_hole(start, end, walk);
 
 		pfn = pmd_pfn(pmd) + pte_index(addr);
 		flag |= pmd_write(pmd) ? HMM_PFN_WRITE : 0;
@@ -462,7 +447,7 @@ again:
 		pfns[i] = 0;
 
 		if (pte_none(pte)) {
-			pfns[i] = HMM_PFN_EMPTY;
+			pfns[i] = 0;
 			if (hmm_vma_walk->fault)
 				goto fault;
 			continue;
@@ -513,8 +498,8 @@ again:
 
 fault:
 		pte_unmap(ptep);
-		/* Fault all pages in range */
-		return hmm_vma_walk_clear(start, end, walk);
+		/* Fault any virtual address we were asked to fault */
+		return hmm_vma_walk_hole(start, end, walk);
 	}
 	pte_unmap(ptep - 1);