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

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commit 2e4d88009f 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.")
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Janosch Frank
2017-03-02 15:23:42 +01:00
committed by Greg Kroah-Hartman
parent 61fbad6a28
commit b0e85701a7
1 changed files with 18 additions and 1 deletions
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19
arch/s390/mm/pgtable.c
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@@ -1237,11 +1237,28 @@ EXPORT_SYMBOL_GPL(s390_reset_cmma);
*/
bool gmap_test_and_clear_dirty(unsigned long address, struct gmap *gmap)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
spinlock_t *ptl;
bool dirty = false;
pte = get_locked_pte(gmap->mm, address, &ptl);
pgd = pgd_offset(gmap->mm, address);
pud = pud_alloc(gmap->mm, pgd, address);
if (!pud)
return false;
pmd = pmd_alloc(gmap->mm, pud, address);
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;
pte = pte_alloc_map_lock(gmap->mm, pmd, address, &ptl);
if (unlikely(!pte))
return false;