dax: remove VM_MIXEDMAP for fsdax and device dax

This patch is reworked from an earlier patch that Dan has posted:
https://patchwork.kernel.org/patch/10131727/

VM_MIXEDMAP is used by dax to direct mm paths like vm_normal_page() that
the memory page it is dealing with is not typical memory from the linear
map.  The get_user_pages_fast() path, since it does not resolve the vma,
is already using {pte,pmd}_devmap() as a stand-in for VM_MIXEDMAP, so we
use that as a VM_MIXEDMAP replacement in some locations.  In the cases
where there is no pte to consult we fallback to using vma_is_dax() to
detect the VM_MIXEDMAP special case.

Now that we have explicit driver pfn_t-flag opt-in/opt-out for
get_user_pages() support for DAX we can stop setting VM_MIXEDMAP.  This
also means we no longer need to worry about safely manipulating vm_flags
in a future where we support dynamically changing the dax mode of a
file.

DAX should also now be supported with madvise_behavior(), vma_merge(),
and copy_page_range().

This patch has been tested against ndctl unit test.  It has also been
tested against xfstests commit: 625515d using fake pmem created by
memmap and no additional issues have been observed.

Link: http://lkml.kernel.org/r/152847720311.55924.16999195879201817653.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/mm/hmm.c b/mm/hmm.c
index de7b6bf77201..f40e8add84b5 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -676,7 +676,8 @@ int hmm_vma_get_pfns(struct hmm_range *range)
 		return -EINVAL;
 
 	/* FIXME support hugetlb fs */
-	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL)) {
+	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
+			vma_is_dax(vma)) {
 		hmm_pfns_special(range);
 		return -EINVAL;
 	}
@@ -849,7 +850,8 @@ int hmm_vma_fault(struct hmm_range *range, bool block)
 		return -EINVAL;
 
 	/* FIXME support hugetlb fs */
-	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL)) {
+	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
+			vma_is_dax(vma)) {
 		hmm_pfns_special(range);
 		return -EINVAL;
 	}