[qemu-xen staging-4.13] hbitmap: handle set/reset with zero length

[patchbot@xxxxxxx]

commit c0b35d87de345bd3b59a44c604b247a0497f2fc0
Author:     Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
AuthorDate: Fri Oct 11 12:07:07 2019 +0300
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon Nov 4 08:31:55 2019 -0600

    hbitmap: handle set/reset with zero length
    
    Passing zero length to these functions leads to unpredicted results.
    Zero-length set/reset may occur in active-mirror, on zero-length write
    (which is unlikely, but not guaranteed to never happen).
    
    Let's just do nothing on zero-length request.
    
    Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
    Message-id: 20191011090711.19940-2-vsementsov@xxxxxxxxxxxxx
    Reviewed-by: Max Reitz <mreitz@xxxxxxxxxx>
    Cc: qemu-stable@xxxxxxxxxx
    Signed-off-by: Max Reitz <mreitz@xxxxxxxxxx>
    (cherry picked from commit fed33bd175f663cc8c13f8a490a4f35a19756cfe)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 util/hbitmap.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/util/hbitmap.c b/util/hbitmap.c
index 71c6ba2c52..c059313b9e 100644
--- a/util/hbitmap.c
+++ b/util/hbitmap.c
@@ -387,6 +387,10 @@ void hbitmap_set(HBitmap *hb, uint64_t start, uint64_t 
count)
     uint64_t first, n;
     uint64_t last = start + count - 1;
 
+    if (count == 0) {
+        return;
+    }
+
     trace_hbitmap_set(hb, start, count,
                       start >> hb->granularity, last >> hb->granularity);
 
@@ -478,6 +482,10 @@ void hbitmap_reset(HBitmap *hb, uint64_t start, uint64_t 
count)
     uint64_t last = start + count - 1;
     uint64_t gran = 1ULL << hb->granularity;
 
+    if (count == 0) {
+        return;
+    }
+
     assert(QEMU_IS_ALIGNED(start, gran));
     assert(QEMU_IS_ALIGNED(count, gran) || (start + count == hb->orig_size));
 
--
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