[PATCH 3.13 079/103] KVM: s390/mm: try a cow on read only pages for key ops

[Kamal Mostafa]

3.13.11.8 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christian Borntraeger <borntraeger at de.ibm.com>

commit ab3f285f227fec62868037e9b1b1fd18294a83b8 upstream.

The PFMF instruction handler  blindly wrote the storage key even if
the page was mapped R/O in the host. Lets try a COW before continuing
and bail out in case of errors.

Signed-off-by: Christian Borntraeger <borntraeger at de.ibm.com>
Reviewed-by: Dominik Dingel <dingel at linux.vnet.ibm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/s390/mm/pgtable.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index e794c88..9cffb96 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -810,11 +810,21 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
 	pte_t *ptep;
 
 	down_read(&mm->mmap_sem);
+retry:
 	ptep = get_locked_pte(current->mm, addr, &ptl);
 	if (unlikely(!ptep)) {
 		up_read(&mm->mmap_sem);
 		return -EFAULT;
 	}
+	if (!(pte_val(*ptep) & _PAGE_INVALID) &&
+	     (pte_val(*ptep) & _PAGE_PROTECT)) {
+			pte_unmap_unlock(*ptep, ptl);
+			if (fixup_user_fault(current, mm, addr, FAULT_FLAG_WRITE)) {
+				up_read(&mm->mmap_sem);
+				return -EFAULT;
+			}
+			goto retry;
+		}
 
 	new = old = pgste_get_lock(ptep);
 	pgste_val(new) &= ~(PGSTE_GR_BIT | PGSTE_GC_BIT |
-- 
1.9.1