[RFC v2 PATCH 3/7] thp: make MADV_HUGEPAGE check for mm->def_flags

[Gerald Schaefer <gerald.schaefer@de.ibm.com>]

This adds a check to hugepage_madvise(), to refuse MADV_HUGEPAGE
if VM_NOHUGEPAGE is set in mm->def_flags. On s390, the VM_NOHUGEPAGE
flag will be set in mm->def_flags for kvm processes, to prevent any
future thp mappings. In order to also prevent MADV_HUGEPAGE on such an
mm, hugepage_madvise() should check mm->def_flags.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
---
 mm/huge_memory.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8bac516..f39cb03 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1464,6 +1464,8 @@ out:
 int hugepage_madvise(struct vm_area_struct *vma,
 		     unsigned long *vm_flags, int advice)
 {
+	struct mm_struct *mm = vma->vm_mm;
+
 	switch (advice) {
 	case MADV_HUGEPAGE:
 		/*
@@ -1471,6 +1473,8 @@ int hugepage_madvise(struct vm_area_struct *vma,
 		 */
 		if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
 			return -EINVAL;
+		if (mm->def_flags & VM_NOHUGEPAGE)
+			return -EINVAL;
 		*vm_flags &= ~VM_NOHUGEPAGE;
 		*vm_flags |= VM_HUGEPAGE;
 		/*
-- 
1.7.11.5