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
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)
