Re: [PATCH] kvmgt: Hold struct kvm reference

[Jike Song <jike.song@intel.com>]

On 03/20/2017 10:38 AM, Alex Williamson wrote:
> The kvmgt code keeps a pointer to the struct kvm associated with the
> device, but doesn't actually hold a reference to it.  If we do unclean
> shutdown testing (ie. killing the user process), then we can see the
> kvm association to the device unset, which causes kvmgt to trigger a
> device release via a work queue.  Naturally we cannot guarantee that
> the cached struct kvm pointer is still valid at this point without
> holding a reference.  The observed failure in this case is a stuck
> cpu trying to acquire the spinlock from the invalid reference, but
> other failure modes are clearly possible.  Hold a reference to avoid
> this.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> Cc: stable@vger.kernel.org #v4.10
> Cc: Jike Song <jike.song@intel.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
> Cc: Zhi Wang <zhi.a.wang@intel.com>
> ---

Reviewed-by: Jike Song <jike.song@intel.com>

Thanks for the fix!

--
Thanks,
Jike

>  drivers/gpu/drm/i915/gvt/kvmgt.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index 84d801638ede..142b8bd4ba6b 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -1324,6 +1324,7 @@ static int kvmgt_guest_init(struct mdev_device *mdev)
>  	vgpu->handle = (unsigned long)info;
>  	info->vgpu = vgpu;
>  	info->kvm = kvm;
> +	kvm_get_kvm(info->kvm);
>  
>  	kvmgt_protect_table_init(info);
>  	gvt_cache_init(vgpu);
> @@ -1343,6 +1344,7 @@ static bool kvmgt_guest_exit(struct kvmgt_guest_info *info)
>  	}
>  
>  	kvm_page_track_unregister_notifier(info->kvm, &info->track_node);
> +	kvm_put_kvm(info->kvm);
>  	kvmgt_protect_table_destroy(info);
>  	gvt_cache_destroy(info->vgpu);
>  	vfree(info);
>