[Intel-gfx] [bug report] drm/i915/gvt/kvmgt: add vfio/mdev support to KVMGT

[Dan Carpenter]

Hello Jike Song,

The patch 659643f7d814: "drm/i915/gvt/kvmgt: add vfio/mdev support to
KVMGT" from Dec 8, 2016, leads to the following static checker
warning:

	drivers/gpu/drm/i915/gvt/kvmgt.c:969 intel_vgpu_ioctl()
	warn: calling kfree() when 'caps.buf' is always NULL.

drivers/gpu/drm/i915/gvt/kvmgt.c
   909          } else if (cmd == VFIO_DEVICE_GET_REGION_INFO) {
   910                  struct vfio_region_info info;
   911                  struct vfio_info_cap caps = { .buf = NULL, .size = 0 };
                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Set here.

   912                  int i, ret;
   913                  struct vfio_region_info_cap_sparse_mmap *sparse = NULL;
   914                  size_t size;
   915                  int nr_areas = 1;
   916                  int cap_type_id;
   917  
   918                  minsz = offsetofend(struct vfio_region_info, offset);
   919  
   920                  if (copy_from_user(&info, (void __user *)arg, minsz))
   921                          return -EFAULT;
   922  
   923                  if (info.argsz < minsz)
   924                          return -EINVAL;
   925  
   926                  switch (info.index) {
   927                  case VFIO_PCI_CONFIG_REGION_INDEX:
   928                          info.offset = VFIO_PCI_INDEX_TO_OFFSET(info.index);
   929                          info.size = INTEL_GVT_MAX_CFG_SPACE_SZ;
   930                          info.flags = VFIO_REGION_INFO_FLAG_READ |
   931                                       VFIO_REGION_INFO_FLAG_WRITE;
   932                          break;
   933                  case VFIO_PCI_BAR0_REGION_INDEX:
   934                          info.offset = VFIO_PCI_INDEX_TO_OFFSET(info.index);
   935                          info.size = vgpu->cfg_space.bar[info.index].size;
   936                          if (!info.size) {
   937                                  info.flags = 0;
   938                                  break;
   939                          }
   940  
   941                          info.flags = VFIO_REGION_INFO_FLAG_READ |
   942                                       VFIO_REGION_INFO_FLAG_WRITE;
   943                          break;
   944                  case VFIO_PCI_BAR1_REGION_INDEX:
   945                          info.offset = VFIO_PCI_INDEX_TO_OFFSET(info.index);
   946                          info.size = 0;
   947                          info.flags = 0;
   948                          break;
   949                  case VFIO_PCI_BAR2_REGION_INDEX:
   950                          info.offset = VFIO_PCI_INDEX_TO_OFFSET(info.index);
   951                          info.flags = VFIO_REGION_INFO_FLAG_CAPS |
   952                                          VFIO_REGION_INFO_FLAG_MMAP |
   953                                          VFIO_REGION_INFO_FLAG_READ |
   954                                          VFIO_REGION_INFO_FLAG_WRITE;
   955                          info.size = gvt_aperture_sz(vgpu->gvt);
   956  
   957                          size = sizeof(*sparse) +
   958                                          (nr_areas * sizeof(*sparse->areas));
   959                          sparse = kzalloc(size, GFP_KERNEL);
   960                          if (!sparse)
   961                                  return -ENOMEM;
   962  
   963                          sparse->nr_areas = nr_areas;
   964                          cap_type_id = VFIO_REGION_INFO_CAP_SPARSE_MMAP;
   965                          sparse->areas[0].offset =
   966                                          PAGE_ALIGN(vgpu_aperture_offset(vgpu));
   967                          sparse->areas[0].size = vgpu_aperture_sz(vgpu);
   968                          if (!caps.buf) {
                                     ^^^^^^^^
It's always NULL.

   969                                  kfree(caps.buf);

Freeing NULL is pointless.

   970                                  caps.buf = NULL;
   971                                  caps.size = 0;

These were already zeroed out at the start of the function.  What was
intended here?  Probably you could just delete these lines.

   972                          }
   973                          break;
   974  
   975                  case VFIO_PCI_BAR3_REGION_INDEX ... VFIO_PCI_BAR5_REGION_INDEX:

regards,
dan carpenter