Save RING_HEAD into vgpu reg when vgpu switched out and report
it's value back to guest.
v6: addressed comment for ring head wrap count support. (Zhenyu)
v5: ring head wrap count support.
v4: updated HEAD/TAIL with guest value, not host value. (Yan Zhao)
v3: save RING HEAD/TAIL vgpu reg in save_ring_hw_state. (Zhenyu Wang)
v2: save RING_TAIL as well during vgpu mmio switch to meet ring_is_idle
condition. (Fred Gao)
v1: based on input from Weinan. (Weinan Li)
[zhenyuw: Include this fix for possible future guest kernel that
would utilize RING_HEAD for hangcheck.]
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Xiaolin Zhang <xiaolin.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
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