[Xen-changelog] [qemu-xen master] vfio: Handle zero-length sparse mmap ranges

[patchbot@xxxxxxx]

commit 24acf72b9a291cebfd05f2ecdf3a982ac01e6291
Author:     Alex Williamson <alex.williamson@xxxxxxxxxx>
AuthorDate: Mon Oct 31 09:53:03 2016 -0600
Commit:     Alex Williamson <alex.williamson@xxxxxxxxxx>
CommitDate: Mon Oct 31 09:53:03 2016 -0600

    vfio: Handle zero-length sparse mmap ranges
    
    As reported in the link below, user has a PCI device with a 4KB BAR
    which contains the MSI-X table.  This seems to hit a corner case in
    the kernel where the region reports being mmap capable, but the sparse
    mmap information reports a zero sized range.  It's not entirely clear
    that the kernel is incorrect in doing this, but regardless, we need
    to handle it.  To do this, fill our mmap array only with non-zero
    sized sparse mmap entries and add an error return from the function
    so we can tell the difference between nr_mmaps being zero based on
    sparse mmap info vs lack of sparse mmap info.
    
    NB, this doesn't actually change the behavior of the device, it only
    removes the scary "Failed to mmap ... Performance may be slow" error
    message.  We cannot currently create an mmap over the MSI-X table.
    
    Link: 
http://lists.nongnu.org/archive/html/qemu-discuss/2016-10/msg00009.html
    Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
---
 hw/vfio/common.c | 36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index c764cb3..f528309 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -610,16 +610,16 @@ vfio_get_region_info_cap(struct vfio_region_info *info, 
uint16_t id)
     return NULL;
 }
 
-static void vfio_setup_region_sparse_mmaps(VFIORegion *region,
-                                           struct vfio_region_info *info)
+static int vfio_setup_region_sparse_mmaps(VFIORegion *region,
+                                          struct vfio_region_info *info)
 {
     struct vfio_info_cap_header *hdr;
     struct vfio_region_info_cap_sparse_mmap *sparse;
-    int i;
+    int i, j;
 
     hdr = vfio_get_region_info_cap(info, VFIO_REGION_INFO_CAP_SPARSE_MMAP);
     if (!hdr) {
-        return;
+        return -ENODEV;
     }
 
     sparse = container_of(hdr, struct vfio_region_info_cap_sparse_mmap, 
header);
@@ -627,16 +627,24 @@ static void vfio_setup_region_sparse_mmaps(VFIORegion 
*region,
     trace_vfio_region_sparse_mmap_header(region->vbasedev->name,
                                          region->nr, sparse->nr_areas);
 
-    region->nr_mmaps = sparse->nr_areas;
-    region->mmaps = g_new0(VFIOMmap, region->nr_mmaps);
+    region->mmaps = g_new0(VFIOMmap, sparse->nr_areas);
 
-    for (i = 0; i < region->nr_mmaps; i++) {
-        region->mmaps[i].offset = sparse->areas[i].offset;
-        region->mmaps[i].size = sparse->areas[i].size;
-        trace_vfio_region_sparse_mmap_entry(i, region->mmaps[i].offset,
-                                            region->mmaps[i].offset +
-                                            region->mmaps[i].size);
+    for (i = 0, j = 0; i < sparse->nr_areas; i++) {
+        trace_vfio_region_sparse_mmap_entry(i, sparse->areas[i].offset,
+                                            sparse->areas[i].offset +
+                                            sparse->areas[i].size);
+
+        if (sparse->areas[i].size) {
+            region->mmaps[j].offset = sparse->areas[i].offset;
+            region->mmaps[j].size = sparse->areas[i].size;
+            j++;
+        }
     }
+
+    region->nr_mmaps = j;
+    region->mmaps = g_realloc(region->mmaps, j * sizeof(VFIOMmap));
+
+    return 0;
 }
 
 int vfio_region_setup(Object *obj, VFIODevice *vbasedev, VFIORegion *region,
@@ -665,9 +673,9 @@ int vfio_region_setup(Object *obj, VFIODevice *vbasedev, 
VFIORegion *region,
             region->flags & VFIO_REGION_INFO_FLAG_MMAP &&
             !(region->size & ~qemu_real_host_page_mask)) {
 
-            vfio_setup_region_sparse_mmaps(region, info);
+            ret = vfio_setup_region_sparse_mmaps(region, info);
 
-            if (!region->nr_mmaps) {
+            if (ret) {
                 region->nr_mmaps = 1;
                 region->mmaps = g_new0(VFIOMmap, region->nr_mmaps);
                 region->mmaps[0].offset = 0;
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#master

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