[PATCH v3 01/14] mm: Convert pXd_devmap checks to vma_is_dax

[Alistair Popple]

Currently dax is the only user of pmd and pud mapped ZONE_DEVICE
pages. Therefore page walkers that want to exclude DAX pages can check
pmd_devmap or pud_devmap. However soon dax will no longer set PFN_DEV,
meaning dax pages are mapped as normal pages.

Ensure page walkers that currently use pXd_devmap to skip DAX pages
continue to do so by adding explicit checks of the VMA instead.

Remove vma_is_dax() check from mm/userfaultfd.c as validate_move_areas()
will already skip DAX VMA's on account of them not being anonymous.

The check in userfaultfd_must_wait() is also redundant as
vma_can_userfault() should have already filtered out dax vma's.

For HMM the pud_devmap check seems unnecessary as there is no reason we
shouldn't be able to handle any leaf PUD here so remove it also.

Signed-off-by: Alistair Popple <apopple at nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg at nvidia.com>
Reviewed-by: Dan Williams <dan.j.williams at intel.com>

---

Changes from v2:

 - Drop checks vma_is_dax checks in userfaultd and hmm

Changes from v1:

 - Remove vma_is_dax() check from mm/userfaultfd.c as
   validate_move_areas() will already skip DAX VMA's on account of them
   not being anonymous.
---
 fs/userfaultfd.c | 2 +-
 mm/hmm.c         | 2 +-
 mm/userfaultfd.c | 6 ------
 3 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index ef054b3..aef4e86 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -304,7 +304,7 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
 		goto out;
 
 	ret = false;
-	if (!pmd_present(_pmd) || pmd_devmap(_pmd))
+	if (!pmd_present(_pmd))
 		goto out;
 
 	if (pmd_trans_huge(_pmd)) {
diff --git a/mm/hmm.c b/mm/hmm.c
index feac861..d0c5c35 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -441,7 +441,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 		return hmm_vma_walk_hole(start, end, -1, walk);
 	}
 
-	if (pud_leaf(pud) && pud_devmap(pud)) {
+	if (pud_leaf(pud)) {
 		unsigned long i, npages, pfn;
 		unsigned int required_fault;
 		unsigned long *hmm_pfns;
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 58b3ad6..8395db2 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1818,12 +1818,6 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
 
 		ptl = pmd_trans_huge_lock(src_pmd, src_vma);
 		if (ptl) {
-			if (pmd_devmap(*src_pmd)) {
-				spin_unlock(ptl);
-				err = -ENOENT;
-				break;
-			}
-
 			/* Check if we can move the pmd without splitting it. */
 			if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
 			    !pmd_none(dst_pmdval)) {
-- 
git-series 0.9.1