On 2013-10-02 20:47, Jan Kiszka wrote:
> On 2013-09-30 11:08, Jan Kiszka wrote:
>> On 2013-09-26 17:04, Paolo Bonzini wrote:
>>> Il 16/09/2013 10:11, Arthur Chunqi Li ha scritto:
>>>> This patch contains the following two changes:
>>>> 1. Fix the bug in nested preemption timer support. If vmexit L2->L0
>>>> with some reasons not emulated by L1, preemption timer value should
>>>> be save in such exits.
>>>> 2. Add support of "Save VMX-preemption timer value" VM-Exit controls
>>>> to nVMX.
>>>>
>>>> With this patch, nested VMX preemption timer features are fully
>>>> supported.
>>>>
>>>> Signed-off-by: Arthur Chunqi Li <yzt356@xxxxxxxxx>
>>>> ---
>>>> ChangeLog to v4:
>>>> Format changes and remove a flag in nested_vmx.
>>>> arch/x86/include/uapi/asm/msr-index.h | 1 +
>>>> arch/x86/kvm/vmx.c | 44 +++++++++++++++++++++++++++++++--
>>>> 2 files changed, 43 insertions(+), 2 deletions(-)
>>>
>>> Hi all,
>>>
>>> the test fails for me if the preemption timer value is set to a value
>>> that is above ~2000 (which means ~65000 TSC cycles on this machine).
>>> The preemption timer seems to count faster than what is expected, for
>>> example only up to 4 million cycles if you set it to one million.
>>> So, I am leaving the patch out of kvm/queue for now, until I can
>>> test it on more processors.
>>
>> I've done some measurements with the help of ftrace on the time it takes
>> to let the preemption timer trigger (no adjustments via Arthur's patch
>> were involved): On my Core i7-620M, the preemption timer seems to tick
>> almost 10 times faster than spec and scale value (5) suggests. I've
>> loaded a value of 100000, and it took about 130 µs until I got a vmexit
>> with reason PREEMPTION_TIMER (no other exists in between).
>>
>> qemu-system-x86-13765 [003] 298562.966079: bprint: prepare_vmcs02: preempt val 100000
>> qemu-system-x86-13765 [003] 298562.966083: kvm_entry: vcpu 0
>> qemu-system-x86-13765 [003] 298562.966212: kvm_exit: reason PREEMPTION_TIMER rip 0x401fea info 0 0
>>
>> That's a frequency of ~769 MHz. The TSC ticks at 2.66 GHz. But 769 MHz *
>> 2^5 is 24.6 GHz. I've read the spec several times, but it seems pretty
>> clear on this. It just doesn't match reality. Very strange.
>
> ...but documented: I found an related errata for my processor (AAT59)
> and also for Xeon 5500 (AAK139). At least current Haswell generation is
> no affected. I can test the patch on a Haswell board I have at work
> later this week.
To complete this story: Arthur's patch works fine on a non-broken CPU
(here: i7-4770S).
Arthur, find some fix-ups for your test case below. It avoids printing
from within L2 as this could deadlock when the timer fires and L1 then
tries to print something. Also, it disables the preemption timer on
leave so that it cannot fire later on again. If you want to fold this
into your patch, feel free. Otherwise I can post a separate patch on
top.
Jan
diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
index 4372878..66a4201 100644
--- a/x86/vmx_tests.c
+++ b/x86/vmx_tests.c
@@ -141,6 +141,9 @@ void preemption_timer_init()
preempt_val = 10000000;
vmcs_write(PREEMPT_TIMER_VALUE, preempt_val);
preempt_scale = rdmsr(MSR_IA32_VMX_MISC) & 0x1F;
+
+ if (!(ctrl_exit_rev.clr & EXI_SAVE_PREEMPT))
+ printf("\tSave preemption value is not supported\n");
}
void preemption_timer_main()
@@ -150,9 +153,7 @@ void preemption_timer_main()
printf("\tPreemption timer is not supported\n");
return;
}
- if (!(ctrl_exit_rev.clr & EXI_SAVE_PREEMPT))
- printf("\tSave preemption value is not supported\n");
- else {
+ if (ctrl_exit_rev.clr & EXI_SAVE_PREEMPT) {
set_stage(0);
vmcall();
if (get_stage() == 1)
@@ -161,8 +162,8 @@ void preemption_timer_main()
while (1) {
if (((rdtsc() - tsc_val) >> preempt_scale)
> 10 * preempt_val) {
- report("Preemption timer", 0);
- break;
+ set_stage(2);
+ vmcall();
}
}
}
@@ -183,7 +184,7 @@ int preemption_timer_exit_handler()
report("Preemption timer", 0);
else
report("Preemption timer", 1);
- return VMX_TEST_VMEXIT;
+ break;
case VMX_VMCALL:
switch (get_stage()) {
case 0:
@@ -195,24 +196,29 @@ int preemption_timer_exit_handler()
EXI_SAVE_PREEMPT) & ctrl_exit_rev.clr;
vmcs_write(EXI_CONTROLS, ctrl_exit);
}
- break;
+ vmcs_write(GUEST_RIP, guest_rip + insn_len);
+ return VMX_TEST_RESUME;
case 1:
if (vmcs_read(PREEMPT_TIMER_VALUE) >= preempt_val)
report("Save preemption value", 0);
else
report("Save preemption value", 1);
+ vmcs_write(GUEST_RIP, guest_rip + insn_len);
+ return VMX_TEST_RESUME;
+ case 2:
+ report("Preemption timer", 0);
break;
default:
printf("Invalid stage.\n");
print_vmexit_info();
- return VMX_TEST_VMEXIT;
+ break;
}
- vmcs_write(GUEST_RIP, guest_rip + insn_len);
- return VMX_TEST_RESUME;
+ break;
default:
printf("Unknown exit reason, %d\n", reason);
print_vmexit_info();
}
+ vmcs_write(PIN_CONTROLS, vmcs_read(PIN_CONTROLS) & ~PIN_PREEMPT);
return VMX_TEST_VMEXIT;
}
--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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