From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries to emulate invalid guest state task-switch: kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 kvm_emulate_insn: 42000:0:0f 0b (0x2) kvm_emulate_insn: 42000:0:0f 0b (0x2) failed kvm_inj_exception: #UD (0x0) kvm_entry: vcpu 0 kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 kvm_emulate_insn: 42000:0:0f 0b (0x2) kvm_emulate_insn: 42000:0:0f 0b (0x2) failed kvm_inj_exception: #UD (0x0) ...................... It appears that the task-switch emulation updates rflags (and vm86 flag) only after the segments are loaded, causing vmx->emulation_required to be set, when in fact invalid guest state emulation is not needed. This patch fixes it by updating vmx->emulation_required after the rflags (and vm86 flag) is updated in task-switch emulation. Suggested-by: Nadav Amit <nadav.amit@xxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> Cc: Nadav Amit <nadav.amit@xxxxxxxxx> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> --- 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 f50cbfd..70270a2 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -6255,6 +6255,7 @@ static int handle_task_switch(struct kvm_vcpu *vcpu) * TODO: What about debug traps on tss switch? * Are we supposed to inject them and update dr6? */ + vmx->emulation_required = emulation_required(vcpu); return 1; } -- 2.7.4
