[Qemu-devel] [PATCH 03/11] vfio-pci: Unmap and retry DMA mapping

[Alex Williamson <alex.williamson@redhat.com>]

Occasionally we get regions added that overlap with existing mappings.
These always seems to be in the VGA ROM range.  VFIO returns EBUSY
for these mapping attempts.  We can try a little harder and assume
that the latest mapping is correct by removing any overlapping ranges
and retrying the original request.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

 hw/vfio_pci.c |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/hw/vfio_pci.c b/hw/vfio_pci.c
index 2d89d17..7413f2d 100644
--- a/hw/vfio_pci.c
+++ b/hw/vfio_pci.c
@@ -819,12 +819,19 @@ static int vfio_dma_map(VFIOContainer *container, target_phys_addr_t iova,
         map.flags |= VFIO_DMA_MAP_FLAG_WRITE;
     }
 
-    if (ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map)) {
-        DPRINTF("VFIO_MAP_DMA: %d\n", -errno);
-        return -errno;
+    /*
+     * Try the mapping, if it fails with EBUSY, unmap the region and try
+     * again.  This shouldn't be necessary, but we sometimes see it in
+     * the the VGA ROM space.
+     */
+    if (ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0 ||
+        (errno == EBUSY && vfio_dma_unmap(container, iova, size) == 0 &&
+         ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0)) {
+        return 0;
     }
 
-    return 0;
+    DPRINTF("VFIO_MAP_DMA: %d\n", -errno);
+    return -errno;
 }
 
 static void vfio_listener_dummy1(MemoryListener *listener)