[Intel-gfx] [PATCH 1/2] drm/i915: Don't deballoon unused ggtt drm_mm_node in linux guest

[Zhenyu Wang]

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 at vger.kernel.org
> Signed-off-by: Xiong Zhang <xiong.y.zhang at 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 at linux.intel.com>

-- 
Open Source Technology Center, Intel ltd.

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