On 02/01/2018 03:19 PM, Konrad Rzeszutek Wilk wrote:
.snip..
+/* Is SPEC_CTRL intercepted for the currently running vCPU? */
+static bool spec_ctrl_intercepted(struct kvm_vcpu *vcpu)
+{
+ unsigned long *msr_bitmap;
+ int f = sizeof(unsigned long);
+
+ if (!cpu_has_vmx_msr_bitmap())
+ return true;
+
+ msr_bitmap = is_guest_mode(vcpu) ?
+ to_vmx(vcpu)->nested.vmcs02.msr_bitmap :
+ to_vmx(vcpu)->vmcs01.msr_bitmap;
+
+ return !!test_bit(MSR_IA32_SPEC_CTRL, msr_bitmap + 0x800 / f);
+}
+
..snip..
@@ -3359,6 +3393,34 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct
msr_data *msr_info)
case MSR_IA32_TSC:
kvm_write_tsc(vcpu, msr_info);
break;
+ case MSR_IA32_SPEC_CTRL:
+ if (!msr_info->host_initiated &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_IBRS) &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
+ return 1;
+
+ vmx->spec_ctrl_used = true;
+
+ /* The STIBP bit doesn't fault even if it's not advertised */
+ if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP))
+ return 1;
+
+ vmx->spec_ctrl = data;
+
+ /*
+ * When it's written (to non-zero) for the first time, pass
+ * it through. This means we don't have to take the perf
.. But only if it is a nested guest (as you have && is_guest_mode).
Do you want to update the comment a bit?
+ * hit of saving it on vmexit for the common case of guests
+ * that don't use it.
+ */
+ if (cpu_has_vmx_msr_bitmap() && data &&
+ spec_ctrl_intercepted(vcpu) &&
+ is_guest_mode(vcpu))
^^^^^^^^^^^^^^^^^^ <=== here
Would it be perhaps also good to mention the complexity of how
we ought to be handling L1 and L2 guests in the commit?
We are all stressed and I am sure some of us haven't gotten much
sleep - but it can help in say three months when some unluckly new
soul is trying to understand this and gets utterly confused.
Yup, I will go through the patches and add as much details as possible.
And yes, the is_guest_mode(vcpu) here is inverted :D I blame the late
night :)
+ vmx_disable_intercept_for_msr(
+ vmx->vmcs01.msr_bitmap,
+ MSR_IA32_SPEC_CTRL,
+ MSR_TYPE_RW);
+ break;
case MSR_IA32_PRED_CMD:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_IBPB) &&
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