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Subject[PATCH] KVM: nVMX: Fix CR4 after VMLAUNCH/VMRESUME failure
From: Wanpeng Li <>

In L0, Haswell client host:

nested_vmx_exit_reflected failed vm entry 7
WARNING: CPU: 6 PID: 6797 at kvm/arch/x86/kvm//vmx.c:6206 handle_desc+0x2d/0x40 [kvm_intel]
CPU: 6 PID: 6797 Comm: qemu-system-x86 Tainted: G W OE 4.15.0+ #4
RIP: 0010:handle_desc+0x2d/0x40 [kvm_intel]
Call Trace:
vmx_handle_exit+0xbd/0xe20 [kvm_intel]
? kvm_arch_vcpu_ioctl_run+0xcde/0x1c00 [kvm]
kvm_arch_vcpu_ioctl_run+0xd5a/0x1c00 [kvm]
kvm_vcpu_ioctl+0x3e9/0x720 [kvm]
? kvm_vcpu_ioctl+0x3e9/0x720 [kvm]
? __fget+0xfc/0x210
? __fget+0xfc/0x210
? __fget+0x11d/0x210

This can be reproduced by running kvm-unit-tests/ vmx_controls in
L1. UMIP CPUID bit is exposed to the L1 UMIP aware guest since it is emulated
by enabling descriptor-table exits on L0. There is a vmentry fail when
L0 tries to run L2 directly, the L1 guest architectural CR4 is not restored
after this failure since commit 4f350c6dbcb (kvm: nVMX: Handle deferred early
VMLAUNCH/VMRESUME failure properly). The L2 is kvm-unit-tests which will not
write CR4 w/ X86_CR4_UMIP bit. After another L1 access descriptor vmexit, we
check L2's architectural CR4 instead of L1's architectural CR4. This patch
fixes it by restoring L1's architectural CR4 after L0's VMLAUNCH/VMRESUME

Cc: Paolo Bonzini <>
Cc: Radim Krčmář <>
Signed-off-by: Wanpeng Li <>
arch/x86/kvm/vmx.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 23789c9..9fc0492 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -11633,6 +11633,7 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);

+ vcpu->arch.cr4 = vmcs12->host_cr4;
load_vmcs12_mmu_host_state(vcpu, vmcs12);

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