[PATCH mm-unstable] Revert "mm/khugepaged: remove redundant transhuge_vma_suitable() check"

["Zach O'Keefe" <zokeefe@google.com>]

A pmd should not cross a VMA boundary, which is normally enforced by
vma_adjust_trans_huge(), and assumed by e.g. __split_huge_pmd_locked().

In this regard, the transhuge_vma_suitable() check in
hugepage_vma_check() is not redundant with the transhuge_vma_suitable()
check previously in hugepage_vma_revalidate().

The former validates the VMA itself, and checks that *some* memory
in the VMA is suitable to collapse while the latter validates if
collapsing at a specific address is suitable.  By removing the check on
the faulting address, we've inadvertently allowed collapse of a pmd that
can cross vma->vm_end. Revert this change.

Fixes: 143776e7512e ("mm/khugepaged: remove redundant transhuge_vma_suitable() check")
Signed-off-by: Zach O'Keefe <zokeefe@google.com>
---
Apologies, Andrew. I think you've put the series description into this
first patch (thank you).  Do you mind moving it into the next patch in the
series,
"mm: khugepaged: don't carry huge page to the next loop for !CONFIG_NUMA"?
Note that the "mm: userspace hugepage collapse, v7" series doesn't actually
depend on this patch, it was just a cleanup (and thus perhaps I shouldn't have
included it in the series in the first place).
---
 mm/khugepaged.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 2db6d0dd2981..69990dacde14 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -855,6 +855,8 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
 	if (!vma)
 		return SCAN_VMA_NULL;
 
+	if (!transhuge_vma_suitable(vma, address))
+		return SCAN_ADDRESS_RANGE;
 	if (!hugepage_vma_check(vma, vma->vm_flags, false, false,
 				cc->is_khugepaged))
 		return SCAN_VMA_CHECK;
-- 
2.37.0.170.g444d1eabd0-goog