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Subject[PATCH 1/3] Revert "thp: make MADV_HUGEPAGE check for mm->def_flags"
This reverts commit 8e72033f2a489b6c98c4e3c7cc281b1afd6cb85c, and adds
in code to fix up any issues caused by the revert.

The revert is necessary because hugepage_madvise would return -EINVAL
when VM_NOHUGEPAGE is set, which will break subsequent chunks of this
patch set.

Here's a snip of an e-mail from Gerald detailing the original purpose
of this code, and providing justification for the revert:

The intent of 8e72033f2a48 was to guard against any future programming
errors that may result in an madvice(MADV_HUGEPAGE) on guest mappings,
which would crash the kernel.

Martin suggested adding the bit to arch/s390/mm/pgtable.c, if 8e72033f2a48
was to be reverted, because that check will also prevent a kernel crash
in the case described above, it will now send a SIGSEGV instead.

This would now also allow to do the madvise on other parts, if needed,
so it is a more flexible approach. One could also say that it would have
been better to do it this way right from the beginning...

Signed-off-by: Alex Thorlton <>
Suggested-by: Oleg Nesterov <>
Cc: Gerald Schaefer <>
Cc: Martin Schwidefsky <>
Cc: Heiko Carstens <>
Cc: Christian Borntraeger <>
Cc: Andrew Morton <>
Cc: Paolo Bonzini <>
Cc: "Kirill A. Shutemov" <>
Cc: Mel Gorman <>
Cc: Rik van Riel <>
Cc: Ingo Molnar <>
Cc: Peter Zijlstra <>
Cc: Andrea Arcangeli <>
Cc: Oleg Nesterov <>
Cc: "Eric W. Biederman" <>
Cc: Alexander Viro <>

arch/s390/mm/pgtable.c | 3 +++
mm/huge_memory.c | 4 ----
2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 3584ed9..a87cdb4 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -504,6 +504,9 @@ static int gmap_connect_pgtable(unsigned long address, unsigned long segment,
if (!pmd_present(*pmd) &&
__pte_alloc(mm, vma, pmd, vmaddr))
return -ENOMEM;
+ /* large pmds cannot yet be handled */
+ if (pmd_large(*pmd))
+ return -EFAULT;
/* pmd now points to a valid segment table entry. */
rmap = kmalloc(sizeof(*rmap), GFP_KERNEL|__GFP_REPEAT);
if (!rmap)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 82166bf..a4310a5 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1968,8 +1968,6 @@ out:
int hugepage_madvise(struct vm_area_struct *vma,
unsigned long *vm_flags, int advice)
- struct mm_struct *mm = vma->vm_mm;
switch (advice) {
@@ -1977,8 +1975,6 @@ 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;

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