4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Janosch Frank <frankja@xxxxxxxxxxxxxxxxxx> commit 2e4d88009f57057df7672fa69a32b5224af54d37 upstream. While we can technically not run huge page guests right now, we can setup a guest with huge pages. Trying to migrate it will trigger a VM_BUG_ON and, if the kernel is not configured to panic on a BUG, it will happily try to work on non-existing page table entries. With this patch, we always return "dirty" if we encounter a large page when migrating. This at least fixes the immediate problem until we have proper handling for both kind of pages. Fixes: 15f36eb ("KVM: s390: Add proper dirty bitmap support to S390 kvm.") Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxxxxxxx> Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/s390/mm/pgtable.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) --- a/arch/s390/mm/pgtable.c +++ b/arch/s390/mm/pgtable.c @@ -606,12 +606,29 @@ void ptep_zap_key(struct mm_struct *mm, bool test_and_clear_guest_dirty(struct mm_struct *mm, unsigned long addr) { spinlock_t *ptl; + pgd_t *pgd; + pud_t *pud; + pmd_t *pmd; pgste_t pgste; pte_t *ptep; pte_t pte; bool dirty; - ptep = get_locked_pte(mm, addr, &ptl); + pgd = pgd_offset(mm, addr); + pud = pud_alloc(mm, pgd, addr); + if (!pud) + return false; + pmd = pmd_alloc(mm, pud, addr); + if (!pmd) + return false; + /* We can't run guests backed by huge pages, but userspace can + * still set them up and then try to migrate them without any + * migration support. + */ + if (pmd_large(*pmd)) + return true; + + ptep = pte_alloc_map_lock(mm, pmd, addr, &ptl); if (unlikely(!ptep)) return false;