From: "Aneesh Kumar K.V" aneesh.kumar@linux.ibm.com Subject: mm/hugetlb: fix kernel crash with hugetlb mremap

This fixes the below crash:

kernel BUG at include/linux/mm.h:2373! cpu 0x5d: Vector: 700 (Program Check) at [c00000003c6e76e0] pc: c000000000581a54: pmd_to_page+0x54/0x80 lr: c00000000058d184: move_hugetlb_page_tables+0x4e4/0x5b0 sp: c00000003c6e7980 msr: 9000000000029033 current = 0xc00000003bd8d980 paca = 0xc000200fff610100 irqmask: 0x03 irq_happened: 0x01 pid = 9349, comm = hugepage-mremap kernel BUG at include/linux/mm.h:2373! [link register ] c00000000058d184 move_hugetlb_page_tables+0x4e4/0x5b0 [c00000003c6e7980] c00000000058cecc move_hugetlb_page_tables+0x22c/0x5b0 (unreliable) [c00000003c6e7a90] c00000000053b78c move_page_tables+0xdbc/0x1010 [c00000003c6e7bd0] c00000000053bc34 move_vma+0x254/0x5f0 [c00000003c6e7c90] c00000000053c790 sys_mremap+0x7c0/0x900 [c00000003c6e7db0] c00000000002c450 system_call_exception+0x160/0x2c0

the kernel can't use huge_pte_offset before it set the pte entry because a page table lookup check for huge PTE bit in the page table to differentiate between a huge pte entry and a pointer to pte page. A huge_pte_alloc won't mark the page table entry huge and hence kernel should not use huge_pte_offset after a huge_pte_alloc.

Link: https://lkml.kernel.org/r/20220211063221.99293-1-aneesh.kumar@linux.ibm.com Fixes: 550a7d60bd5e ("mm, hugepages: add mremap() support for hugepage backed vma") Signed-off-by: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Reviewed-by: Mike Kravetz mike.kravetz@oracle.com Reviewed-by: Mina Almasry almasrymina@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/hugetlb.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-fix-kernel-crash-with-hugetlb-mremap +++ a/mm/hugetlb.c @@ -4851,14 +4851,13 @@ again: }

static void move_huge_pte(struct vm_area_struct *vma, unsigned long old_addr, - unsigned long new_addr, pte_t *src_pte) + unsigned long new_addr, pte_t *src_pte, pte_t *dst_pte) { struct hstate *h = hstate_vma(vma); struct mm_struct *mm = vma->vm_mm; - pte_t *dst_pte, pte; spinlock_t *src_ptl, *dst_ptl; + pte_t pte;

- dst_pte = huge_pte_offset(mm, new_addr, huge_page_size(h)); dst_ptl = huge_pte_lock(h, mm, dst_pte); src_ptl = huge_pte_lockptr(h, mm, src_pte);

@@ -4917,7 +4916,7 @@ int move_hugetlb_page_tables(struct vm_a if (!dst_pte) break;

- move_huge_pte(vma, old_addr, new_addr, src_pte); + move_huge_pte(vma, old_addr, new_addr, src_pte, dst_pte); } flush_tlb_range(vma, old_end - len, old_end); mmu_notifier_invalidate_range_end(&range); _