mm: vmalloc fix lazy unmapping cache aliasing

Jim Radford has reported that the vmap subsystem rewrite was sometimes
causing his VIVT ARM system to behave strangely (seemed like going into
infinite loops trying to fault in pages to userspace).

We determined that the problem was most likely due to a cache aliasing
issue.  flush_cache_vunmap was only being called at the moment the page
tables were to be taken down, however with lazy unmapping, this can happen
after the page has subsequently been freed and allocated for something
else.  The dangling alias may still have dirty data attached to it.

The fix for this problem is to do the cache flushing when the caller has
called vunmap -- it would be a bug for them to write anything else to the
mapping at that point.

That appeared to solve Jim's problems.

Reported-by: Jim Radford <[email protected]>
Signed-off-by: Nick Piggin <[email protected]>
Cc: Russell King <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/vmalloc.c

@@ -77,7 +77,6 @@ static void vunmap_page_range(unsigned long addr, unsigned long end)
 
 	BUG_ON(addr >= end);
 	pgd = pgd_offset_k(addr);
-	flush_cache_vunmap(addr, end);
 	do {
 		next = pgd_addr_end(addr, end);
 		if (pgd_none_or_clear_bad(pgd))
@@ -543,16 +542,26 @@ static void purge_vmap_area_lazy(void)
 }
 
 /*
- * Free and unmap a vmap area
+ * Free and unmap a vmap area, caller ensuring flush_cache_vunmap had been
+ * called for the correct range previously.
  */
-static void free_unmap_vmap_area(struct vmap_area *va)
+static void free_unmap_vmap_area_noflush(struct vmap_area *va)
 {
 	va->flags |= VM_LAZY_FREE;
 	atomic_add((va->va_end - va->va_start) >> PAGE_SHIFT, &vmap_lazy_nr);
 	if (unlikely(atomic_read(&vmap_lazy_nr) > lazy_max_pages()))
 		try_purge_vmap_area_lazy();
 }
 
+/*
+ * Free and unmap a vmap area
+ */
+static void free_unmap_vmap_area(struct vmap_area *va)
+{
+	flush_cache_vunmap(va->va_start, va->va_end);
+	free_unmap_vmap_area_noflush(va);
+}
+
 static struct vmap_area *find_vmap_area(unsigned long addr)
 {
 	struct vmap_area *va;
@@ -734,7 +743,7 @@ static void free_vmap_block(struct vmap_block *vb)
 	spin_unlock(&vmap_block_tree_lock);
 	BUG_ON(tmp != vb);
 
-	free_unmap_vmap_area(vb->va);
+	free_unmap_vmap_area_noflush(vb->va);
 	call_rcu(&vb->rcu_head, rcu_free_vb);
 }
 
@@ -796,6 +805,9 @@ static void vb_free(const void *addr, unsigned long size)
 
 	BUG_ON(size & ~PAGE_MASK);
 	BUG_ON(size > PAGE_SIZE*VMAP_MAX_ALLOC);
+
+	flush_cache_vunmap((unsigned long)addr, (unsigned long)addr + size);
+
 	order = get_order(size);
 
 	offset = (unsigned long)addr & (VMAP_BLOCK_SIZE - 1);