[qemu-xen stable-4.13] util/hbitmap: strict hbitmap_reset

[patchbot@xxxxxxx]

commit fcd7cba6acb7344aca70f5f8ec16626e817b35a5
Author:     Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
AuthorDate: Tue Aug 6 18:26:11 2019 +0300
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon Nov 4 08:31:40 2019 -0600

    util/hbitmap: strict hbitmap_reset
    
    hbitmap_reset has an unobvious property: it rounds requested region up.
    It may provoke bugs, like in recently fixed write-blocking mode of
    mirror: user calls reset on unaligned region, not keeping in mind that
    there are possible unrelated dirty bytes, covered by rounded-up region
    and information of this unrelated "dirtiness" will be lost.
    
    Make hbitmap_reset strict: assert that arguments are aligned, allowing
    only one exception when @start + @count == hb->orig_size. It's needed
    to comfort users of hbitmap_next_dirty_area, which cares about
    hb->orig_size.
    
    Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
    Reviewed-by: Max Reitz <mreitz@xxxxxxxxxx>
    Message-Id: <20190806152611.280389-1-vsementsov@xxxxxxxxxxxxx>
    [Maintainer edit: Max's suggestions from on-list. --js]
    [Maintainer edit: Eric's suggestion for aligned macro. --js]
    Signed-off-by: John Snow <jsnow@xxxxxxxxxx>
    (cherry picked from commit 48557b138383aaf69c2617ca9a88bfb394fc50ec)
    *prereq for fed33bd175f663cc8c13f8a490a4f35a19756cfe
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 include/qemu/hbitmap.h | 5 +++++
 tests/test-hbitmap.c   | 2 +-
 util/hbitmap.c         | 4 ++++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
index 4afbe6292e..1bf944ca3d 100644
--- a/include/qemu/hbitmap.h
+++ b/include/qemu/hbitmap.h
@@ -132,6 +132,11 @@ void hbitmap_set(HBitmap *hb, uint64_t start, uint64_t 
count);
  * @count: Number of bits to reset.
  *
  * Reset a consecutive range of bits in an HBitmap.
+ * @start and @count must be aligned to bitmap granularity. The only exception
+ * is resetting the tail of the bitmap: @count may be equal to hb->orig_size -
+ * @start, in this case @count may be not aligned. The sum of @start + @count 
is
+ * allowed to be greater than hb->orig_size, but only if @start < hb->orig_size
+ * and @start + @count = ALIGN_UP(hb->orig_size, granularity).
  */
 void hbitmap_reset(HBitmap *hb, uint64_t start, uint64_t count);
 
diff --git a/tests/test-hbitmap.c b/tests/test-hbitmap.c
index 592d8219db..2be56d1597 100644
--- a/tests/test-hbitmap.c
+++ b/tests/test-hbitmap.c
@@ -423,7 +423,7 @@ static void test_hbitmap_granularity(TestHBitmapData *data,
     hbitmap_test_check(data, 0);
     hbitmap_test_set(data, 0, 3);
     g_assert_cmpint(hbitmap_count(data->hb), ==, 4);
-    hbitmap_test_reset(data, 0, 1);
+    hbitmap_test_reset(data, 0, 2);
     g_assert_cmpint(hbitmap_count(data->hb), ==, 2);
 }
 
diff --git a/util/hbitmap.c b/util/hbitmap.c
index bcc0acdc6a..71c6ba2c52 100644
--- a/util/hbitmap.c
+++ b/util/hbitmap.c
@@ -476,6 +476,10 @@ void hbitmap_reset(HBitmap *hb, uint64_t start, uint64_t 
count)
     /* Compute range in the last layer.  */
     uint64_t first;
     uint64_t last = start + count - 1;
+    uint64_t gran = 1ULL << hb->granularity;
+
+    assert(QEMU_IS_ALIGNED(start, gran));
+    assert(QEMU_IS_ALIGNED(count, gran) || (start + count == hb->orig_size));
 
     trace_hbitmap_reset(hb, start, count,
                         start >> hb->granularity, last >> hb->granularity);
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.13