On 11/07/2017 17:54, Radim Krčmář wrote: > 2017-07-11 00:13-0700, Wanpeng Li: >> 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); > > Hm, so the problem happened because changes to rflags can flip the value > of emulation_required(). I would add this line to vmx_set_rflags() to > make sure that we fixed everything, thanks. Note that there is some extra complication, because emulation_required is expensive and you'll want to run it only when EFLAGS.VM changes. Paolo
