[PATCH 4/4] Check whether the new THP is poisoned before it is mappedto APL.

[Hidetoshi Seto]

If the new THP is poisoned after the 4K pages are copied to it
and mapped to APL, APL will be killed by kernel with SIGBUS signal.

There is not much doubt that it is a right behavior. But we can
do our best to reduce the impact of the poisoned THP to the least.

So add final poison check for the new THP before the THP is mapped
to APL. If check find a poison, back to 4K pages and trash the THP.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx>
Signed-off-by: Jin Dongming <jin.dongming@xxxxxxxxxxxxxxxxxx>
---
 mm/huge_memory.c |   14 ++++++++++++--
 1 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 6345279..9aed3a8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1776,13 +1776,14 @@ static void collapse_huge_page(struct mm_struct *mm,
 {
 	pgd_t *pgd;
 	pud_t *pud;
-	pmd_t *pmd, _pmd;
+	pmd_t *pmd, _pmd, old_pmd;
 	pte_t *pte;
 	pgtable_t pgtable;
 	struct page *new_page;
 	spinlock_t *ptl;
 	int isolated;
 	unsigned long hstart, hend;
+	struct page *p;
 
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 #ifndef CONFIG_NUMA
@@ -1873,6 +1874,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 	 * to avoid the risk of CPU bugs in that area.
 	 */
 	_pmd = pmdp_clear_flush_notify(vma, address, pmd);
+	old_pmd = _pmd;
 	spin_unlock(&mm->page_table_lock);
 
 	spin_lock(ptl);
@@ -1904,7 +1906,6 @@ static void collapse_huge_page(struct mm_struct *mm,
 	if (__collapse_huge_page_copy(pte, new_page, vma, address) == 0)
 		goto out_poison;
 
-	pte_unmap(pte);
 	__SetPageUptodate(new_page);
 	pgtable = pmd_pgtable(_pmd);
 	VM_BUG_ON(page_count(pgtable) != 1);
@@ -1921,6 +1922,15 @@ static void collapse_huge_page(struct mm_struct *mm,
 	 */
 	smp_wmb();
 
+	for (p = new_page; p < new_page + HPAGE_PMD_NR; p++) {
+		if (PageHWPoison(p)) {
+			_pmd = old_pmd;
+			goto out_poison;
+		}
+	}
+
+	pte_unmap(pte);
+
 	spin_lock(&mm->page_table_lock);
 	BUG_ON(!pmd_none(*pmd));
 	page_add_new_anon_rmap(new_page, vma, address);
-- 
1.7.1


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