s390x/mm: cleanup gmap_pte_op_walk()

Web:        https://git.kernel.org/torvalds/c/9696594158ec43d210137c1b93313efde8f7315a
Commit:     9696594158ec43d210137c1b93313efde8f7315a
Parent:     50c4c4e268a2d7a3e58ebb698ac74da0de40ae36
Refname:    refs/heads/master
Author:     David Hildenbrand <[email protected]>
AuthorDate: Fri Nov 10 16:18:05 2017 +0100
Committer:  Christian Borntraeger <[email protected]>
CommitDate: Tue Jan 16 16:15:16 2018 +0100

    s390x/mm: cleanup gmap_pte_op_walk()
    
    gmap_mprotect_notify() refuses shadow gmaps. Turns out that
    a) gmap_protect_range()
    b) gmap_read_table()
    c) gmap_pte_op_walk()
    
    Are never called for gmap shadows. And never should be. This dates back
    to gmap shadow prototypes where we allowed to call mprotect_notify() on
    the gmap shadow (to get notified about the prefix pages getting removed).
    This is avoided by always getting notified about any change on the gmap
    shadow.
    
    The only real function for walking page tables on shadow gmaps is
    gmap_table_walk().
    
    So, essentially, these functions should never get called and
    gmap_pte_op_walk() can be cleaned up. Add some checks to callers of
    gmap_pte_op_walk().
    
    Signed-off-by: David Hildenbrand <[email protected]>
    Message-Id: <[email protected]>
    Reviewed-by: Janosch Frank <[email protected]>
    Acked-by: Cornelia Huck <[email protected]>
    Signed-off-by: Christian Borntraeger <[email protected]>
---
 arch/s390/mm/gmap.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 05d459b638f5..54cfd51a5a27 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -815,27 +815,17 @@ static inline unsigned long *gmap_table_walk(struct gmap *gmap,
  * @ptl: pointer to the spinlock pointer
  *
  * Returns a pointer to the locked pte for a guest address, or NULL
- *
- * Note: Can also be called for shadow gmaps.
  */
 static pte_t *gmap_pte_op_walk(struct gmap *gmap, unsigned long gaddr,
 			       spinlock_t **ptl)
 {
 	unsigned long *table;
 
-	if (gmap_is_shadow(gmap))
-		spin_lock(&gmap->guest_table_lock);
+	BUG_ON(gmap_is_shadow(gmap));
 	/* Walk the gmap page table, lock and get pte pointer */
 	table = gmap_table_walk(gmap, gaddr, 1); /* get segment pointer */
-	if (!table || *table & _SEGMENT_ENTRY_INVALID) {
-		if (gmap_is_shadow(gmap))
-			spin_unlock(&gmap->guest_table_lock);
+	if (!table || *table & _SEGMENT_ENTRY_INVALID)
 		return NULL;
-	}
-	if (gmap_is_shadow(gmap)) {
-		*ptl = &gmap->guest_table_lock;
-		return pte_offset_map((pmd_t *) table, gaddr);
-	}
 	return pte_alloc_map_lock(gmap->mm, (pmd_t *) table, gaddr, ptl);
 }
 
@@ -889,8 +879,6 @@ static void gmap_pte_op_end(spinlock_t *ptl)
  * -EFAULT if gaddr is invalid (or mapping for shadows is missing).
  *
  * Called with sg->mm->mmap_sem in read.
- *
- * Note: Can also be called for shadow gmaps.
  */
 static int gmap_protect_range(struct gmap *gmap, unsigned long gaddr,
 			      unsigned long len, int prot, unsigned long bits)
@@ -900,6 +888,7 @@ static int gmap_protect_range(struct gmap *gmap, unsigned long gaddr,
 	pte_t *ptep;
 	int rc;
 
+	BUG_ON(gmap_is_shadow(gmap));
 	while (len) {
 		rc = -EAGAIN;
 		ptep = gmap_pte_op_walk(gmap, gaddr, &ptl);
@@ -960,7 +949,8 @@ EXPORT_SYMBOL_GPL(gmap_mprotect_notify);
  * @val: pointer to the unsigned long value to return
  *
  * Returns 0 if the value was read, -ENOMEM if out of memory and -EFAULT
- * if reading using the virtual address failed.
+ * if reading using the virtual address failed. -EINVAL if called on a gmap
+ * shadow.
  *
  * Called with gmap->mm->mmap_sem in read.
  */
@@ -971,6 +961,9 @@ int gmap_read_table(struct gmap *gmap, unsigned long gaddr, unsigned long *val)
 	pte_t *ptep, pte;
 	int rc;
 
+	if (gmap_is_shadow(gmap))
+		return -EINVAL;
+
 	while (1) {
 		rc = -EAGAIN;
 		ptep = gmap_pte_op_walk(gmap, gaddr, &ptl);
--
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