[PATCH] mm: Loosen MADV_NOHUGEPAGE to enable Qemu postcopy on s390

["Jason J. Herne" <jjherne@linux.vnet.ibm.com>]

MADV_NOHUGEPAGE processing is too restrictive. kvm already disables
hugepage but hugepage_madvise() takes the error path when we ask to turn
on the MADV_NOHUGEPAGE bit and the bit is already on. This causes Qemu's
new postcopy migration feature to fail on s390 because its first action is
to madvise the guest address space as NOHUGEPAGE. This patch modifies the
code so that the operation succeeds without error now.

Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
---
 mm/huge_memory.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c29ddeb..62fe06b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2009,7 +2009,7 @@ int hugepage_madvise(struct vm_area_struct *vma,
 		/*
 		 * Be somewhat over-protective like KSM for now!
 		 */
-		if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
+		if (*vm_flags & VM_NO_THP)
 			return -EINVAL;
 		*vm_flags &= ~VM_NOHUGEPAGE;
 		*vm_flags |= VM_HUGEPAGE;
@@ -2025,7 +2025,7 @@ int hugepage_madvise(struct vm_area_struct *vma,
 		/*
 		 * Be somewhat over-protective like KSM for now!
 		 */
-		if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
+		if (*vm_flags & VM_NO_THP)
 			return -EINVAL;
 		*vm_flags &= ~VM_HUGEPAGE;
 		*vm_flags |= VM_NOHUGEPAGE;
-- 
1.9.1

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