| Message ID | 1513924309-3113-1-git-send-email-changbin.du@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Quoting changbin.du@intel.com (2017-12-22 06:31:49) > From: Changbin Du <changbin.du@intel.com> > > 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> > --- > drivers/gpu/drm/i915/i915_memcpy.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/i915_memcpy.c b/drivers/gpu/drm/i915/i915_memcpy.c > index 49a0794..8921f40 100644 > --- 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)) > + /** This isn't a kerneldoc, so just /* for a regular comment. > + * 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); Code checks out, and I believe you that some hypervisor setups may trap those instructions, so Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> We could try and jigger the init order about, but we do need this setup quite early so that we use the knowledge in other setup. Considering that, an explicit check for a hypervisor seems sensible. -Chris
On Fri, Dec 22, 2017 at 11:11:15AM +0000, Chris Wilson wrote: > Quoting changbin.du@intel.com (2017-12-22 06:31:49) > > From: Changbin Du <changbin.du@intel.com> > > > > 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> > > --- > > drivers/gpu/drm/i915/i915_memcpy.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/gpu/drm/i915/i915_memcpy.c b/drivers/gpu/drm/i915/i915_memcpy.c > > index 49a0794..8921f40 100644 > > --- 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)) > > + /** > > This isn't a kerneldoc, so just /* for a regular comment. > Thanks, will update. > > + * 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); > > Code checks out, and I believe you that some hypervisor setups may trap > those instructions, so > > Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> > > We could try and jigger the init order about, but we do need this setup > quite early so that we use the knowledge in other setup. Considering > that, an explicit check for a hypervisor seems sensible. > -Chris And this check is not only for GVTg, but also for physical GPU passthrough. So it is beyong intel_vgpu_active().
diff --git a/drivers/gpu/drm/i915/i915_memcpy.c b/drivers/gpu/drm/i915/i915_memcpy.c index 49a0794..8921f40 100644 --- 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); }