[PATCH 4.10 64/81] drm/i915/kvmgt: Hold struct kvm reference

Greg Kroah-Hartman
2017-04-06T08:56:34Z

From: Alex Williamson <alex.williamson@redhat.com>

commit 93a15b58cfb8a24e666ffca432f19fe65c1cd7d1 upstream.

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: 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>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/i915/gvt/kvmgt.c | 2 ++
1 file changed, 2 insertions(+)

--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -1334,6 +1334,7 @@ static int kvmgt_guest_init(struct 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);
@@ -1353,6 +1354,7 @@ static bool kvmgt_guest_exit(struct kvmg
}

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);