PATCH: nVMX: Better MSR_IA32_FEATURE_CONTROL handling

[Nadav Har'El <nyh@math.technion.ac.il>]

The existing code emulates the guest's use of the IA32_FEATURE_CONTROL MSR
in a way that was enough to run nested VMX guests, but did not fully
conform to the VMX specification, and in particular did not allow a guest
BIOS to prevent the guest OS from using VMX by setting the lock bit on this
MSR.

This patch emulates this MSR better, allowing the guest to lock it, and
verifying its setting on VMXON. Also make sure that this MSR (and of course,
VMXON state) is reset on guest vcpu reset (via SIPI).

Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
Reported-by: Julian Stecklina <js@alien8.de>
---
 arch/x86/kvm/vmx.c |   24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

--- .before/arch/x86/kvm/vmx.c	2012-03-07 17:52:02.000000000 +0200
+++ .after/arch/x86/kvm/vmx.c	2012-03-07 17:52:02.000000000 +0200
@@ -352,6 +352,7 @@ struct nested_vmx {
 	 * we must keep them pinned while L2 runs.
 	 */
 	struct page *apic_access_page;
+	u64 msr_ia32_feature_control;
 };
 
 struct vcpu_vmx {
@@ -1999,7 +2000,7 @@ static int vmx_get_vmx_msr(struct kvm_vc
 
 	switch (msr_index) {
 	case MSR_IA32_FEATURE_CONTROL:
-		*pdata = 0;
+		*pdata = to_vmx(vcpu)->nested.msr_ia32_feature_control;
 		break;
 	case MSR_IA32_VMX_BASIC:
 		/*
@@ -2077,9 +2078,13 @@ static int vmx_set_vmx_msr(struct kvm_vc
 	if (!nested_vmx_allowed(vcpu))
 		return 0;
 
-	if (msr_index == MSR_IA32_FEATURE_CONTROL)
-		/* TODO: the right thing. */
+	if (msr_index == MSR_IA32_FEATURE_CONTROL) {
+		if (to_vmx(vcpu)->nested.msr_ia32_feature_control
+				& FEATURE_CONTROL_LOCKED)
+			return 0;
+		to_vmx(vcpu)->nested.msr_ia32_feature_control = data;
 		return 1;
+	}
 	/*
 	 * No need to treat VMX capability MSRs specially: If we don't handle
 	 * them, handle_wrmsr will #GP(0), which is correct (they are readonly)
@@ -3807,6 +3812,8 @@ static int vmx_vcpu_setup(struct vcpu_vm
 	return 0;
 }
 
+static void free_nested(struct vcpu_vmx *vmx);
+
 static int vmx_vcpu_reset(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -3920,6 +3927,9 @@ static int vmx_vcpu_reset(struct kvm_vcp
 	/* HACK: Don't enable emulation on guest boot/reset */
 	vmx->emulation_required = 0;
 
+	/* Reset nested-VMX settings: */
+	vmx->nested.msr_ia32_feature_control = 0;
+	free_nested(vmx);
 out:
 	return ret;
 }
@@ -5031,6 +5041,14 @@ static int handle_vmon(struct kvm_vcpu *
 		return 1;
 	}
 
+#define VMXON_NEEDED_FEATURES \
+	  (FEATURE_CONTROL_LOCKED | FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX)
+	if ((vmx->nested.msr_ia32_feature_control & VMXON_NEEDED_FEATURES)
+			!= VMXON_NEEDED_FEATURES) {
+		kvm_inject_gp(vcpu, 0);
+		return 1;
+	}
+
 	INIT_LIST_HEAD(&(vmx->nested.vmcs02_pool));
 	vmx->nested.vmcs02_num = 0;
 
-- 
Nadav Har'El                        |                  Wednesday, Mar 7 2012, 
nyh@math.technion.ac.il             |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |In Fortran, God is real unless declared
http://nadav.harel.org.il           |an integer.