From 219af7331f37e0e803688f6c5f7d29bc6204e88e Mon Sep 17 00:00:00 2001
From: Changbin Du <changbin.du@intel.com>
Date: Fri, 22 Dec 2017 14:31:49 +0800
Subject: [PATCH] drm/i915: Do not enable movntdqa optimization in hypervisor guest
Git-commit: 219af7331f37e0e803688f6c5f7d29bc6204e88e
Patch-mainline: v4.16-rc1
References: FATE#322643 bsc#1055900

Our QA reported a problem caused by movntdqa instructions. Currently,
the KVM hypervisor doesn't support VEX-prefix instructions emulation.
If users passthrough a GPU to guest with vfio option 'x-no-mmap=on',
then all access to the BARs will be trapped and emulated. The KVM
hypervisor would raise an inertal error to qemu which cause the guest
killed. (Since 'movntdqa' ins is not supported.)

This patch try not to enable movntdqa optimization if the driver is
running in hypervisor guest.

Signed-off-by: Changbin Du <changbin.du@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1513924309-3113-1-git-send-email-changbin.du@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/i915_memcpy.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/i915_memcpy.c
+++ b/drivers/gpu/drm/i915/i915_memcpy.c
@@ -96,6 +96,11 @@ bool i915_memcpy_from_wc(void *dst, cons
 
 void i915_memcpy_init_early(struct drm_i915_private *dev_priv)
 {
-	if (static_cpu_has(X86_FEATURE_XMM4_1))
+	/*
+	 * Some hypervisors (e.g. KVM) don't support VEX-prefix instructions
+	 * emulation. So don't enable movntdqa in hypervisor guest.
+	 */
+	if (static_cpu_has(X86_FEATURE_XMM4_1) &&
+	    !boot_cpu_has(X86_FEATURE_HYPERVISOR))
 		static_branch_enable(&has_movntdqa);
 }