[RFC PATCH 5/5] dax: re-enable dax pmd mappings

[Dan Williams <dan.j.williams@intel.com>]

Now that the get_user_pages() path knows how to handle dax-pmd mappings,
remove the protections that disabled dax-pmd support.

Test-case from github.com/pmem/ndctl:

    make TESTS=lib/test-dax.sh check

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 fs/Kconfig |    3 ++-
 fs/dax.c   |    8 ++------
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/fs/Kconfig b/fs/Kconfig
index 6ce72d8d1ee1..ad8f4aa4161c 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -50,7 +50,8 @@ config FS_DAX_PMD
 	bool
 	default FS_DAX
 	depends on FS_DAX
-	depends on BROKEN
+	depends on ZONE_DEVICE
+	depends on TRANSPARENT_HUGEPAGE
 
 endif # BLOCK
 
diff --git a/fs/dax.c b/fs/dax.c
index a429a00628c5..6662de3c0bc7 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -573,7 +573,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 	sector_t block;
 	int result = 0;
 
-	/* dax pmd mappings are broken wrt gup and fork */
+	/* dax pmd mappings require pfn_t_devmap() */
 	if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
 		return VM_FAULT_FALLBACK;
 
@@ -692,11 +692,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 			goto fallback;
 		}
 
-		/*
-		 * TODO: teach vmf_insert_pfn_pmd() to support
-		 * 'pte_special' for pmds
-		 */
-		if (pfn_t_has_page(dax.pfn)) {
+		if (!pfn_t_devmap(dax.pfn)) {
 			dax_unmap_atomic(bdev, &dax);
 			reason = "pfn not in memmap";
 			goto fallback;

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