2018-04-05 1:09 GMT+08:00 Paolo Bonzini <pbonz...@redhat.com>: > On 04/04/2018 15:35, Wanpeng Li wrote: >> 2018-04-04 19:59 GMT+08:00 David Hildenbrand <da...@redhat.com>: >>> >>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>>> index 1eb495e..a55ecef 100644 >>>> --- a/arch/x86/kvm/x86.c >>>> +++ b/arch/x86/kvm/x86.c >>>> @@ -146,6 +146,9 @@ bool __read_mostly enable_vmware_backdoor = false; >>>> module_param(enable_vmware_backdoor, bool, S_IRUGO); >>>> EXPORT_SYMBOL_GPL(enable_vmware_backdoor); >>>> >>>> +static bool __read_mostly force_emulation_prefix = false; >>>> +module_param(force_emulation_prefix, bool, S_IRUGO); >>>> + >>>> #define KVM_NR_SHARED_MSRS 16 >>>> >>>> struct kvm_shared_msrs_global { >>>> @@ -4844,6 +4847,21 @@ int handle_ud(struct kvm_vcpu *vcpu) >>>> { >>>> enum emulation_result er; >>>> >>>> + if (force_emulation_prefix) { >>>> + char sig[5]; /* ud2; .ascii "kvm" */ >>>> + struct x86_exception e; >>>> + >>>> + if (kvm_read_guest_virt(&vcpu->arch.emulate_ctxt, >>>> + kvm_get_linear_rip(vcpu), sig, sizeof(sig), >>>> &e)) >>>> + goto emulate_ud; >>>> + >>>> + if (memcmp(sig, "\xf\xbkvm", sizeof(sig)) == 0) { >>>> + kvm_rip_write(vcpu, kvm_rip_read(vcpu) + >>>> sizeof(sig)); >>>> + return emulate_instruction(vcpu, 0) == EMULATE_DONE; >>> >>> What if we would have an invalid instruction here? Shouldn't you handle >>> the emulate_instruction() like below? >>> (e.g. keep a variable with the emulation type (0 vs EMULTYPE_TRAP_UD) >>> and reuse emulate_ud below) >> >> emulate_instruction(vcpu, 0) can handle invalid instruction. > > But David's observation is still better because your code doesn't handle > usermode exits.
My code handles it, return emulate_instruction(vcpu, 0) == EMULATE_DONE, it will return 0 since EMULATE_USER_EXIT == EMULATE_DONE fails. > I've fixed this up. Thanks. The codes similar to my v3 but more beauty. :) I change to this view since Radim's comments to v3 https://www.spinics.net/lists/kvm/msg166999.html Regards, Wanpeng Li