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Commit 2e4d8800 authored by Janosch Frank's avatar Janosch Frank Committed by Martin Schwidefsky
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KVM: s390: Fix guest migration for huge guests resulting in panic 



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: 15f36ebd ("KVM: s390: Add proper dirty bitmap support to S390 kvm.")
Cc: <stable@vger.kernel.org> # 3.16+

Signed-off-by: default avatarJanosch Frank <frankja@linux.vnet.ibm.com>
Acked-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 7afbeb6d

arch/s390/mm/pgtable.c

+18 −1
Original line number Diff line number Diff line
@@ -608,12 +608,29 @@ void ptep_zap_key(struct mm_struct *mm, unsigned long addr, pte_t *ptep) 
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;