[Intel-gfx] [PATCH] drm/i915: Force VT'd workarounds when running as a guest OS

[Chris Wilson]

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 causing 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 at sfritsch.de>
Suggested-by: Stefan Fritsch <sf at sfritsch.de>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Zhenyu Wang <zhenyuw at linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Stefan Fritsch <sf at sfritsch.de>
Cc: stable at vger.kernel.org
---
 drivers/gpu/drm/i915/i915_drv.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1a5729932c81..02a3dac412d8 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/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>
@@ -1760,6 +1762,13 @@ static inline bool intel_vtd_active(void)
 	if (intel_iommu_gfx_mapped)
 		return true;
 #endif
+
+#ifdef CONFIG_HYPERVISOR_GUEST
+	/* Running as a guest, we assume the host is enforcing VT'd */
+	if (x86_hyper_type != X86_HYPER_NATIVE)
+		return true;
+#endif
+
 	return false;
 }
 
-- 
2.20.1