When userspace sets MSR_IA32_FEATURE_CONTROL to 0, make sure we leave
root and non-root mode, fully disabling VMX. The register state of the
VCPU is undefined after this step, so userspace has to set it to a
proper state afterward.
This enables to reboot a VM while it is running some hypervisor code.
Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
---
Even without a QEMU patch, this already enables system reset - the guest
is left in such a broken state that it simply triple-faults and resets
twice. Nevertheless, QEMU patch will follow.
arch/x86/kvm/vmx.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index f90320b..6a0c2fa 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2455,6 +2455,8 @@ static int vmx_get_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
return 1;
}
+static void vmx_leave_nested(struct kvm_vcpu *vcpu);
+
static int vmx_set_vmx_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
{
u32 msr_index = msr_info->index;
@@ -2470,6 +2472,8 @@ static int vmx_set_vmx_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
& FEATURE_CONTROL_LOCKED)
return 0;
to_vmx(vcpu)->nested.msr_ia32_feature_control = data;
+ if (host_initialized && data == 0)
+ vmx_leave_nested(vcpu);
return 1;
}
@@ -8488,6 +8492,16 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu)
}
/*
+ * Forcibly leave nested mode in order to be able to reset the VCPU later on.
+ */
+static void vmx_leave_nested(struct kvm_vcpu *vcpu)
+{
+ if (is_guest_mode(vcpu))
+ nested_vmx_vmexit(vcpu);
+ free_nested(to_vmx(vcpu));
+}
+
+/*
* L1's failure to enter L2 is a subset of a normal exit, as explained in
* 23.7 "VM-entry failures during or after loading guest state" (this also
* lists the acceptable exit-reason and exit-qualification parameters).
--
1.8.1.1.298.ge7eed54
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