drm/i915/gvt: Pin vgpu dma address before using

Dma-buf display uses the vgpu dma address saved in the guest part GGTT
table which is updated by vCPU thread. In host side, when the dma
address is used by qemu ui thread, gvt-g must make sure the dma address
is validated before letting it go to the HW. Invalid guest dma address
will easily cause DMA fault and make GPU hang.

v2: Rebase

Fixes: e546e281d3 ("drm/i915/gvt: Dmabuf support for GVT-g")
Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20191212141342.3417-1-tina.zhang@intel.com

drivers/gpu/drm/i915/gvt/hypercall.h

@@ -62,6 +62,8 @@ struct intel_gvt_mpt {
 				  unsigned long size, dma_addr_t *dma_addr);
 	void (*dma_unmap_guest_page)(unsigned long handle, dma_addr_t dma_addr);
 
+	int (*dma_pin_guest_page)(unsigned long handle, dma_addr_t dma_addr);
+
 	int (*map_gfn_to_mfn)(unsigned long handle, unsigned long gfn,
 			      unsigned long mfn, unsigned int nr, bool map);
 	int (*set_trap_area)(unsigned long handle, u64 start, u64 end,