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KVM: s390: Fix guest migration for huge guests resulting in panic

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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.")
Cc: <stable@vger.kernel.org> # 3.16+

Signed-off-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Janosch Frank 2017-03-02 15:23:42 +01:00 committed by Martin Schwidefsky
parent 7afbeb6df2
commit 2e4d88009f
1 changed files with 18 additions and 1 deletions
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19
arch/s390/mm/pgtable.c
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@ -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;