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)
