2017-07-12 0:09 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: > 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. Agreed. Regards, Wanpeng Li
