drm/i915: Force VT'd workarounds when running as a guest OS

If i915.ko is being used as a passthrough device, it does not know if
the host is using intel_iommu. Mixing the iommu and gfx causes a few
issues (such as scanout overfetch) which we need to workaround inside
the driver, so if we detect we are running under a hypervisor, also
assume the device access is being virtualised.

Reported-by: Stefan Fritsch <sf@sfritsch.de>
Suggested-by: Stefan Fritsch <sf@sfritsch.de>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Stefan Fritsch <sf@sfritsch.de>
Cc: stable@vger.kernel.org
Tested-by: Stefan Fritsch <sf@sfritsch.de>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201019101523.4145-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -33,6 +33,8 @@
 #include <uapi/drm/i915_drm.h>
 #include <uapi/drm/drm_fourcc.h>
 
+#include <asm/hypervisor.h>
+
 #include <linux/io-mapping.h>
 #include <linux/i2c.h>
 #include <linux/i2c-algo-bit.h>
@@ -1761,7 +1763,9 @@ static inline bool intel_vtd_active(void)
 	if (intel_iommu_gfx_mapped)
 		return true;
 #endif
-	return false;
+
+	/* Running as a guest, we assume the host is enforcing VT'd */
+	return !hypervisor_is_type(X86_HYPER_NATIVE);
 }
 
 static inline bool intel_scanout_needs_vtd_wa(struct drm_i915_private *dev_priv)