KVM: nVMX: Allow setting the VMXE bit in CR4
This patch allows the guest to enable the VMXE bit in CR4, which is a
prerequisite to running VMXON.
Whether to allow setting the VMXE bit now depends on the architecture (svm
or vmx), so its checking has moved to kvm_x86_ops->set_cr4(). This function
now returns an int: If kvm_x86_ops->set_cr4() returns 1, __kvm_set_cr4()
will also return 1, and this will cause kvm_set_cr4() will throw a #GP.
Turning on the VMXE bit is allowed only when the nested VMX feature is
enabled, and turning it off is forbidden after a vmxon.
Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3a727ca..eda2cb6 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2121,7 +2121,7 @@
(unsigned long *)&vcpu->arch.regs_dirty);
}
-static void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
+static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
static void ept_update_paging_mode_cr0(unsigned long *hw_cr0,
unsigned long cr0,
@@ -2219,11 +2219,23 @@
vmcs_writel(GUEST_CR3, guest_cr3);
}
-static void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
unsigned long hw_cr4 = cr4 | (to_vmx(vcpu)->rmode.vm86_active ?
KVM_RMODE_VM_CR4_ALWAYS_ON : KVM_PMODE_VM_CR4_ALWAYS_ON);
+ if (cr4 & X86_CR4_VMXE) {
+ /*
+ * To use VMXON (and later other VMX instructions), a guest
+ * must first be able to turn on cr4.VMXE (see handle_vmon()).
+ * So basically the check on whether to allow nested VMX
+ * is here.
+ */
+ if (!nested_vmx_allowed(vcpu))
+ return 1;
+ } else if (to_vmx(vcpu)->nested.vmxon)
+ return 1;
+
vcpu->arch.cr4 = cr4;
if (enable_ept) {
if (!is_paging(vcpu)) {
@@ -2236,6 +2248,7 @@
vmcs_writel(CR4_READ_SHADOW, cr4);
vmcs_writel(GUEST_CR4, hw_cr4);
+ return 0;
}
static void vmx_get_segment(struct kvm_vcpu *vcpu,