Maybe you disabled MWAIT it in the BIOS. Try to read IA32_MISC_ENABLE[18]
(MSR 0x1a0). If it is clear, MWAIT/MONITOR is disabled.
> On Jun 8, 2017, at 8:52 PM, Longpeng (Mike) <longpeng2@xxxxxxxxxx> wrote:
>
>
> On 2017/6/9 11:47, Longpeng (Mike) wrote:
>
>> Hi guys,
>>
>> I wrote a testcase which repeat execute MWAIT insn in kvm-unit-test and I tested
>> it on different hardware, but got different results.
>>
>>
>> 1) cpu: E5620 (hardware don't support MONITOR/MWAIT)
>>
>> This works well because I saw the following info in trace:
>>
>> CPU 0/KVM-7301 [015] .... 1534719.099573: kvm_exit: reason
>> MWAIT_INSTRUCTION rip 0x400387 info 0 0
>> CPU 0/KVM-7301 [015] d... 1534719.099573: kvm_entry: vcpu 0
>> CPU 0/KVM-7301 [015] .... 1534719.099574: kvm_exit: reason
>> MWAIT_INSTRUCTION rip 0x400387 info 0 0
>> CPU 0/KVM-7301 [015] d... 1534719.099574: kvm_entry: vcpu 0
>>
>>
>> 2) cpu: E5-2620 v3 and E5-2690 v4 (both hardwares support MONITOR/MWAIT)
>>
>> This...
>>
>> CPU 0/KVM-1683 [017] .... 4844125.856164: kvm_exit: reason EXCEPTION_NMI
>> rip 0x400382 info 0 80000306
>> CPU 0/KVM-1683 [017] .... 4844125.856166: kvm_emulate_insn: 0:400382:0f
>> 01 c9 (prot64)
>> CPU 0/KVM-1683 [017] .... 4844125.856166: kvm_inj_exception: #UD (0x0)
>> CPU 0/KVM-1683 [017] d... 4844125.856167: kvm_entry: vcpu 0
>>
>
>
> Sorry, I made a mistake, the trace of result 2 is:
>
> CPU 0/KVM-14333 [017] .... 4842658.749717: kvm_exit: reason EXCEPTION_NMI
> rip 0x400387 info 0 80000306
> CPU 0/KVM-14333 [017] .... 4842658.749719: kvm_emulate_insn: 0:400387:0f
> 01 c9 (prot64)
> CPU 0/KVM-14333 [017] .... 4842658.749719: kvm_inj_exception: #UD (0x0)
> CPU 0/KVM-14333 [017] d... 4842658.749720: kvm_entry: vcpu 0
>
>
>> and the kvm-unit-test guest reported:
>>
>> Unhandled exception 6 #UD at ip 0000000000400387
>> error_code=0000 rflags=00010002 cs=00000008
>> rax=0000000000000000 rcx=0000000000000000 rdx=0000000200000000 rbx=0000000000000000
>> rbp=000000000044db60 rsi=0000000000000001 rdi=0000000000004020
>> r8=000000000000000a r9=00000000000003f8 r10=000000000044d1e2 r11=000000000044d1e1
>> r12=0000000000000000 r13=0000000000000000 r14=0000000000000000 r15=0000000000000000
>> cr0=0000000080010011 cr2=0000000000000000 cr3=0000000007fff000 cr4=0000000000000020
>> cr8=0000000000000000
>> STACK: @400387 40028f
>> 0x0000000000400387: mwait at x86/perf_exit.c:17
>> /* "mwait %eax, %ecx;" */
>>> asm volatile(".byte 0x0f, 0x01, 0xc9;"
>> :: "a" (eax), "c" (ecx));
>> (inlined by) main at x86/perf_exit.c:93
>> mb();
>>> mwait(0, 0);
>> mb();
>> 0x000000000040028e: start64 at x86/cstart64.S:206
>> lea __argv(%rip), %rsi
>>> call main
>> mov %eax, %edi
>>
>> In result 2, the trace shows that vcpu is in 64bit protect-mode (the testcase
>> didn't jump to ring3 manually, so it's in ring0), as intel vol2 said the MWAIT
>> will #UD in this situation when:
>>
>> #UD If the current privilege level is not 0.
>> If CPUID.01H:ECX.MONITOR[bit 3] = 0.
>>
>> I think CPUID.01H:ECX.MONITOR does not matter, so I'm so curious about the
>> result 2 .
>>
>> Do you have any idea ? Thanks.
>>
>> PS: Wanpeng tested this on his laptop (maybe the cpu is Core-i7) and it worked
>> well as result 1.
>>
>> kvm version : 4.4.11
>> host kernel : 3.10
>>
>>
>> The testcase is:
>>
>> #include "libcflat.h"
>> #include "smp.h"
>> #include "vm.h"
>> #include "processor.h"
>> #include "desc.h"
>> #include "apic.h"
>> #include "apic-defs.h"
>> #include "asm/barrier.h"
>>
>> [...]
>>
>> static inline void mwait(unsigned long eax, unsigned long ecx)
>> {
>> /* "mwait %eax, %ecx;" */
>> asm volatile(".byte 0x0f, 0x01, 0xc9;"
>> :: "a" (eax), "c" (ecx));
>> }
>>
>> [...]
>>
>> int main(int argc, char **argv)
>> {
>> setup_vm();
>> smp_init();
>>
>> while (test_cnt--) {
>> [...]
>> mwait(0, 0);
>> [...]
>> }
>> [...]
>> }
>>
>>
>
>
> --
> Regards,
> Longpeng(Mike)
