On 2019.08.20 13:46:17 +0800, Xiong Zhang wrote:
The following call trace may exist in linux guest dmesg when guest i915 driver is unloaded. [ 90.776610] [drm:vgt_deballoon_space.isra.0 [i915]] deballoon space: range [0x0 - 0x0] 0 KiB. [ 90.776621] BUG: unable to handle kernel NULL pointer dereference at 00000000000000c0 [ 90.776691] IP: drm_mm_remove_node+0x4d/0x320 [drm] [ 90.776718] PGD 800000012c7d0067 P4D 800000012c7d0067 PUD 138e4c067 PMD 0 [ 90.777091] task: ffff9adab60f2f00 task.stack: ffffaf39c0fe0000 [ 90.777142] RIP: 0010:drm_mm_remove_node+0x4d/0x320 [drm] [ 90.777573] Call Trace: [ 90.777653] intel_vgt_deballoon+0x4c/0x60 [i915] [ 90.777729] i915_ggtt_cleanup_hw+0x121/0x190 [i915] [ 90.777792] i915_driver_unload+0x145/0x180 [i915] [ 90.777856] i915_pci_remove+0x15/0x20 [i915] [ 90.777890] pci_device_remove+0x3b/0xc0 [ 90.777916] device_release_driver_internal+0x157/0x220 [ 90.777945] driver_detach+0x39/0x70 [ 90.777967] bus_remove_driver+0x51/0xd0 [ 90.777990] pci_unregister_driver+0x23/0x90 [ 90.778019] SyS_delete_module+0x1da/0x240 [ 90.778045] entry_SYSCALL_64_fastpath+0x24/0x87 [ 90.778072] RIP: 0033:0x7f34312af067 [ 90.778092] RSP: 002b:00007ffdea3da0d8 EFLAGS: 00000206 [ 90.778297] RIP: drm_mm_remove_node+0x4d/0x320 [drm] RSP: ffffaf39c0fe3dc0 [ 90.778344] ---[ end trace f4b1bc8305fc59dd ]---
Four drm_mm_node are used to reserve guest ggtt space, but some of them may be skipped and not initialised due to space constraints in intel_vgt_balloon(). If drm_mm_remove_node() is called with uninitialized drm_mm_node, the above call trace occurs.
This patch check drm_mm_node's validity before calling drm_mm_remove_node().
Fixes: ff8f797557c7("drm/i915: return the correct usable aperture size under gvt environment") Cc: stable@vger.kernel.org Signed-off-by: Xiong Zhang xiong.y.zhang@intel.com
drivers/gpu/drm/i915/i915_vgpu.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_vgpu.c b/drivers/gpu/drm/i915/i915_vgpu.c index bf2b837..d2fd66f 100644 --- a/drivers/gpu/drm/i915/i915_vgpu.c +++ b/drivers/gpu/drm/i915/i915_vgpu.c @@ -119,6 +119,9 @@ static struct _balloon_info_ bl_info; static void vgt_deballoon_space(struct i915_ggtt *ggtt, struct drm_mm_node *node) {
- if (!node->allocated)
return;- DRM_DEBUG_DRIVER("deballoon space: range [0x%llx - 0x%llx] %llu KiB.\n", node->start, node->start + node->size,
Searching shows this is pretty old one and also with r-b from Chris, but be ignored that nobody picked this up..
I think I hit this once too and tried to fix it another way, but this looks simpler to me.
Acked-by: Zhenyu Wang zhenyuw@linux.intel.com