s390/kvm: Provide function for setting the guest storage key

From time to time we need to set the guest storage key. Lets
provide a helper function that handles the changes with all the
right locking and checking.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index a938b548f07e..74c29d922458 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -771,6 +771,54 @@ static inline void page_table_free_pgste(unsigned long *table)
         __free_page(page);
 }
 
+int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
+                          unsigned long key, bool nq)
+{
+        spinlock_t *ptl;
+        pgste_t old, new;
+        pte_t *ptep;
+
+        down_read(&mm->mmap_sem);
+        ptep = get_locked_pte(current->mm, addr, &ptl);
+        if (unlikely(!ptep)) {
+                up_read(&mm->mmap_sem);
+                return -EFAULT;
+        }
+
+        new = old = pgste_get_lock(ptep);
+        pgste_val(new) &= ~(PGSTE_GR_BIT | PGSTE_GC_BIT |
+                            PGSTE_ACC_BITS | PGSTE_FP_BIT);
+        pgste_val(new) |= (key & (_PAGE_CHANGED | _PAGE_REFERENCED)) << 48;
+        pgste_val(new) |= (key & (_PAGE_ACC_BITS | _PAGE_FP_BIT)) << 56;
+        if (!(pte_val(*ptep) & _PAGE_INVALID)) {
+                unsigned long address, bits;
+                unsigned char skey;
+
+                address = pte_val(*ptep) & PAGE_MASK;
+                skey = page_get_storage_key(address);
+                bits = skey & (_PAGE_CHANGED | _PAGE_REFERENCED);
+                /* Set storage key ACC and FP */
+                page_set_storage_key(address,
+                                (key & (_PAGE_ACC_BITS | _PAGE_FP_BIT)),
+                                !nq);
+
+                /* Merge host changed & referenced into pgste  */
+                pgste_val(new) |= bits << 52;
+                /* Transfer skey changed & referenced bit to kvm user bits */
+                pgste_val(new) |= bits << 45;   /* PGSTE_UR_BIT & PGSTE_UC_BIT */
+        }
+        /* changing the guest storage key is considered a change of the page */
+        if ((pgste_val(new) ^ pgste_val(old)) &
+            (PGSTE_ACC_BITS | PGSTE_FP_BIT | PGSTE_GR_BIT | PGSTE_GC_BIT))
+                pgste_val(new) |= PGSTE_UC_BIT;
+
+        pgste_set_unlock(ptep, new);
+        pte_unmap_unlock(*ptep, ptl);
+        up_read(&mm->mmap_sem);
+        return 0;
+}
+EXPORT_SYMBOL(set_guest_storage_key);
+
 #else /* CONFIG_PGSTE */
 
 static inline unsigned long *page_table_alloc_pgste(struct mm_struct *mm,