Re: [PATCH] mm/rmap: Fix potential pte_unmap on an not mapped pte
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2021-01-28 00:11:27
Also in:
lkml
On Wed, 27 Jan 2021 04:33:49 -0500 Miaohe Lin [off-list ref] wrote:
For PMD-mapped page (usually THP), pvmw->pte is NULL. For PTE-mapped THP, pvmw->pte is mapped. But for HugeTLB pages, pvmw->pte is not mapped and set to the relevant page table entry. So in page_vma_mapped_walk_done(), we may do pte_unmap() for HugeTLB pte which is not mapped. Fix this by checking pvmw->page against PageHuge before trying to do pte_unmap().
What are the runtime consequences of this? Is there a workload which is known to trigger it? IOW, how do we justify a -stable backport of this fix?
quoted hunk ↗ jump to hunk
--- a/include/linux/rmap.h +++ b/include/linux/rmap.h@@ -213,7 +213,8 @@ struct page_vma_mapped_walk { static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw) { - if (pvmw->pte) + /* HugeTLB pte is set to the relevant page table entry without pte_mapped. */ + if (pvmw->pte && !PageHuge(pvmw->page)) pte_unmap(pvmw->pte); if (pvmw->ptl) spin_unlock(pvmw->ptl);-- 2.19.1