drm/i915: Don’t deballoon unused ggtt drm_mm_node in linux guest [Linux 4.19.70]

This Linux kernel change "drm/i915: Don’t deballoon unused ggtt drm_mm_node in linux guest" is included in the Linux 4.19.70 release. This change is authored by Xiong Zhang <xiong.y.zhang [at] intel.com> on Tue Aug 20 13:46:17 2019 +0800. The commit for this change in Linux stable tree is c761533 (patch) which is from upstream commit 0a3dfbb. The same Linux upstream change may have been applied to various maintained Linux releases and you can find all Linux releases containing changes from upstream 0a3dfbb.

drm/i915: Don't deballoon unused ggtt drm_mm_node in linux guest

commit 0a3dfbb5cd9033752639ef33e319c2f2863c713a upstream.

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

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>
Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/1566279978-9659-1-git-send-email-xiong.y.zhang@intel.com
(cherry picked from commit 4776f3529d6b1e47f02904ad1d264d25ea22b27b)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

There are 3 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 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 869cf4a..a6cb3e0 100644
--- a/drivers/gpu/drm/i915/i915_vgpu.c
+++ b/drivers/gpu/drm/i915/i915_vgpu.c
@@ -100,6 +100,9 @@ struct _balloon_info_ {
 static void vgt_deballoon_space(struct i915_ggtt *ggtt,
                struct drm_mm_node *node)
+   if (!drm_mm_node_allocated(node))
+       return;
    DRM_DEBUG_DRIVER("deballoon space: range [0x%llx - 0x%llx] %llu KiB.\n",
             node->start + node->size,

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