drm/i915: Do not enable movntdqa optimization in hypervisor guest

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>

diff --git a/drivers/gpu/drm/i915/i915_memcpy.c b/drivers/gpu/drm/i915/i915_memcpy.c
index 49a079494b689e9ba0c1d7c8746184d021400c7b..79f8ec7563621a86479f2f76ebcab5ddbf6161a4 100644 (file)
--- 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, const void *src, unsigned long len)
 
 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);
 }