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[Qemu-devel] [PATCH RFC 6/8] vfio: ccw: introduce page array interfaces


From: Dong Jia Shi
Subject: [Qemu-devel] [PATCH RFC 6/8] vfio: ccw: introduce page array interfaces
Date: Fri, 29 Apr 2016 14:11:53 +0200

CCW translation requires to pin/unpin sets of mem pages frequently.
Currently we have a lack of support to do this in an efficient way.
So we introduce page_array data structure and helper functions to
handle pin/unpin operations here.

Signed-off-by: Dong Jia Shi <address@hidden>
---
 drivers/vfio/ccw/Makefile   |   2 +-
 drivers/vfio/ccw/ccwchain.c | 128 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 129 insertions(+), 1 deletion(-)
 create mode 100644 drivers/vfio/ccw/ccwchain.c

diff --git a/drivers/vfio/ccw/Makefile b/drivers/vfio/ccw/Makefile
index ea14ca9..ac62330 100644
--- a/drivers/vfio/ccw/Makefile
+++ b/drivers/vfio/ccw/Makefile
@@ -1,2 +1,2 @@
-vfio-ccw-y := vfio_ccw.o
+vfio-ccw-y := vfio_ccw.o ccwchain.o
 obj-$(CONFIG_VFIO_CCW) += vfio-ccw.o
diff --git a/drivers/vfio/ccw/ccwchain.c b/drivers/vfio/ccw/ccwchain.c
new file mode 100644
index 0000000..03b4e82
--- /dev/null
+++ b/drivers/vfio/ccw/ccwchain.c
@@ -0,0 +1,128 @@
+/*
+ * ccwchain interfaces
+ *
+ * Copyright IBM Corp. 2016
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License (version 2 only)
+ * as published by the Free Software Foundation.
+ *
+ * Author(s): Dong Jia Shi <address@hidden>
+ *            Xiao Feng Ren <address@hidden>
+ */
+
+#include <linux/mm.h>
+#include <linux/slab.h>
+
+struct page_array {
+       u64                     hva;
+       int                     nr;
+       struct page             **items;
+};
+
+struct page_arrays {
+       struct page_array       *parray;
+       int                     nr;
+};
+
+/*
+ * Helpers to operate page_array.
+ */
+/*
+ * page_array_pin() - pin user pages in memory
+ * @p: page_array on which to perform the operation
+ *
+ * Attempt to pin user pages in memory.
+ *
+ * Usage of page_array:
+ * @p->hva      starting user address. Assigned by caller.
+ * @p->nr       number of pages from @p->hva to pin. Assigned by caller.
+ *              number of pages pinned. Assigned by callee.
+ * @p->items    array that receives pointers to the pages pinned. Allocated by
+ *              caller.
+ *
+ * Returns:
+ *   Number of pages pinned on success. If @p->nr is 0 or negative, returns 0.
+ *   If no pages were pinned, returns -errno.
+ */
+static int page_array_pin(struct page_array *p)
+{
+       int i, nr;
+
+       nr = get_user_pages_fast(p->hva, p->nr, 1, p->items);
+       if (nr <= 0) {
+               p->nr = 0;
+               return nr;
+       } else if (nr != p->nr) {
+               for (i = 0; i < nr; i++)
+                       put_page(p->items[i]);
+               p->nr = 0;
+               return -ENOMEM;
+       }
+
+       return nr;
+}
+
+/* Unpin the items before releasing the memory. */
+static void page_array_items_unpin_free(struct page_array *p)
+{
+       int i;
+
+       for (i = 0; i < p->nr; i++)
+               put_page(p->items[i]);
+
+       p->nr = 0;
+       kfree(p->items);
+}
+
+/* Alloc memory for items, then pin pages with them. */
+static int page_array_items_alloc_pin(u64 hva,
+                                     unsigned int len,
+                                     struct page_array *p)
+{
+       int ret;
+
+       if (!len || p->nr)
+               return -EINVAL;
+
+       p->hva = hva;
+
+       p->nr = ((hva & ~PAGE_MASK) + len + (PAGE_SIZE - 1)) >> PAGE_SHIFT;
+       if (!p->nr)
+               return -EINVAL;
+
+       p->items = kcalloc(p->nr, sizeof(*p->items), GFP_KERNEL);
+       if (!p->items)
+               return -ENOMEM;
+
+       ret = page_array_pin(p);
+       if (ret <= 0)
+               kfree(p->items);
+
+       return ret;
+}
+
+static int page_arrays_init(struct page_arrays *ps, int nr)
+{
+       ps->parray = kcalloc(nr, sizeof(*ps->parray), GFP_KERNEL);
+       if (!ps->parray) {
+               ps->nr = 0;
+               return -ENOMEM;
+       }
+
+       ps->nr = nr;
+       return 0;
+}
+
+static void page_arrays_unpin_free(struct page_arrays *ps)
+{
+       int i;
+
+       for (i = 0; i < ps->nr; i++)
+               page_array_items_unpin_free(ps->parray + i);
+
+       kfree(ps->parray);
+
+       ps->parray = NULL;
+       ps->nr = 0;
+}
-- 
2.6.6




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