s390/kvm: simplify set_guest_storage_key

Git commit ab3f285f227fec62868037e9b1b1fd18294a83b8
"KVM: s390/mm: try a cow on read only pages for key ops"
added a fixup_user_fault to set_guest_storage_key force a copy on
write if the page is mapped read-only. This is supposed to fix the
problem of differing storage keys for shared mappings, e.g. the
empty_zero_page.
But if the storage key is set before the pte is mapped the storage
key update is done on the pgste. A later fault will happily map the
shared page with the key from the pgste.

Eventually git commit 2faee8ff9dc6f4bfe46f6d2d110add858140fb20
"s390/mm: prevent and break zero page mappings in case of storage keys"
fixed this problem for the empty_zero_page. The commit makes sure that
guests enabled for storage keys will not use the empty_zero_page at all.

As the call to fixup_user_fault in set_guest_storage_key depends on the
order of the storage key operation vs. the fault that maps the pte
it does not really fix anything. Just remove it.

Reviewed-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 5109827883acaefc6afc0ac913956fcb79f8f8a0..6acd7174fe750e70be0559636537d35f98c1aab8 100644 (file)
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -809,30 +809,13 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
        spinlock_t *ptl;
        pgste_t old, new;
        pte_t *ptep;
-       bool unlocked;
 
        down_read(&mm->mmap_sem);
-retry:
-       unlocked = false;
        ptep = get_locked_pte(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);
-               /*
-                * We do not really care about unlocked. We will retry either
-                * way. But this allows fixup_user_fault to enable userfaultfd.
-                */
-               if (fixup_user_fault(current, mm, addr, FAULT_FLAG_WRITE,
-                                    &unlocked)) {
-                       up_read(&mm->mmap_sem);
-                       return -EFAULT;
-               }
-               goto retry;
-       }
 
        new = old = pgste_get_lock(ptep);
        pgste_val(new) &= ~(PGSTE_GR_BIT | PGSTE_GC_BIT |