s390/mm: shadow pages with real guest requested protection

We really want to avoid manually handling protection for nested
virtualization. By shadowing pages with the protection the guest asked us
for, the SIE can handle most protection-related actions for us (e.g.
special handling for MVPG) and we can directly forward protection
exceptions to the guest.

PTEs will now always be shadowed with the correct _PAGE_PROTECT flag.
Unshadowing will take care of any guest changes to the parent PTE and
any host changes to the host PTE. If the host PTE doesn't have the
fitting access rights or is not available, we have to fix it up.

Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 7 insertions, 9 deletions

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 5b02583fbf4c..293130b5aee7 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -463,29 +463,27 @@ int ptep_force_prot(struct mm_struct *mm, unsigned long addr,
 }
 
 int ptep_shadow_pte(struct mm_struct *mm, unsigned long saddr,
-		    pte_t *sptep, pte_t *tptep, int write)
+		    pte_t *sptep, pte_t *tptep, pte_t pte)
 {
 	pgste_t spgste, tpgste;
 	pte_t spte, tpte;
 	int rc = -EAGAIN;
 
+	if (!(pte_val(*tptep) & _PAGE_INVALID))
+		return 0;	/* already shadowed */
 	spgste = pgste_get_lock(sptep);
 	spte = *sptep;
 	if (!(pte_val(spte) & _PAGE_INVALID) &&
-	    !(pte_val(spte) & _PAGE_PROTECT)) {
-		rc = 0;
-		if (!(pte_val(*tptep) & _PAGE_INVALID))
-			/* Update existing mapping */
-			ptep_flush_direct(mm, saddr, tptep);
-		else
-			rc = 1;
+	    !((pte_val(spte) & _PAGE_PROTECT) &&
+	      !(pte_val(pte) & _PAGE_PROTECT))) {
 		pgste_val(spgste) |= PGSTE_VSIE_BIT;
 		tpgste = pgste_get_lock(tptep);
 		pte_val(tpte) = (pte_val(spte) & PAGE_MASK) |
-			(write ? 0 : _PAGE_PROTECT);
+				(pte_val(pte) & _PAGE_PROTECT);
 		/* don't touch the storage key - it belongs to parent pgste */
 		tpgste = pgste_set_pte(tptep, tpgste, tpte);
 		pgste_set_unlock(tptep, tpgste);
+		rc = 1;
 	}
 	pgste_set_unlock(sptep, spgste);
 	return rc;