Re: [Qemu-devel] [PATCH] kvm: notify host when guest paniced

[Wen Congyang]

At 02/29/2012 05:36 PM, Gleb Natapov Wrote:
> On Wed, Feb 29, 2012 at 09:08:52AM +0800, Wen Congyang wrote:
>> At 02/28/2012 06:45 PM, Gleb Natapov Wrote:
>>> On Tue, Feb 28, 2012 at 11:19:47AM +0100, Jan Kiszka wrote:
>>>> On 2012-02-28 10:42, Wen Congyang wrote:
>>>>> At 02/28/2012 05:34 PM, Jan Kiszka Wrote:
>>>>>> On 2012-02-28 09:23, Wen Congyang wrote:
>>>>>>> At 02/27/2012 11:08 PM, Jan Kiszka Wrote:
>>>>>>>> On 2012-02-27 04:01, Wen Congyang wrote:
>>>>>>>>> We can know the guest is paniced when the guest runs on xen.
>>>>>>>>> But we do not have such feature on kvm. This patch implemnts
>>>>>>>>> this feature, and the implementation is the same as xen:
>>>>>>>>> register panic notifier, and call hypercall when the guest
>>>>>>>>> is paniced.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Wen Congyang <address@hidden>
>>>>>>>>> ---
>>>>>>>>>  arch/x86/kernel/kvm.c    |   12 ++++++++++++
>>>>>>>>>  arch/x86/kvm/svm.c       |    8 ++++++--
>>>>>>>>>  arch/x86/kvm/vmx.c       |    8 ++++++--
>>>>>>>>>  arch/x86/kvm/x86.c       |   13 +++++++++++--
>>>>>>>>>  include/linux/kvm.h      |    1 +
>>>>>>>>>  include/linux/kvm_para.h |    1 +
>>>>>>>>>  6 files changed, 37 insertions(+), 6 deletions(-)
>>>>>>>>>
>>>>>>>>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
>>>>>>>>> index f0c6fd6..b928d1d 100644
>>>>>>>>> --- a/arch/x86/kernel/kvm.c
>>>>>>>>> +++ b/arch/x86/kernel/kvm.c
>>>>>>>>> @@ -331,6 +331,17 @@ static struct notifier_block kvm_pv_reboot_nb = {
>>>>>>>>>       .notifier_call = kvm_pv_reboot_notify,
>>>>>>>>>  };
>>>>>>>>>  
>>>>>>>>> +static int
>>>>>>>>> +kvm_pv_panic_notify(struct notifier_block *nb, unsigned long code, 
>>>>>>>>> void *unused)
>>>>>>>>> +{
>>>>>>>>> +     kvm_hypercall0(KVM_HC_GUEST_PANIC);
>>>>>>>>> +     return NOTIFY_DONE;
>>>>>>>>> +}
>>>>>>>>> +
>>>>>>>>> +static struct notifier_block kvm_pv_panic_nb = {
>>>>>>>>> +     .notifier_call = kvm_pv_panic_notify,
>>>>>>>>> +};
>>>>>>>>> +
>>>>>>>>
>>>>>>>> You should split up host and guest-side changes.
>>>>>>>>
>>>>>>>>>  static u64 kvm_steal_clock(int cpu)
>>>>>>>>>  {
>>>>>>>>>       u64 steal;
>>>>>>>>> @@ -417,6 +428,7 @@ void __init kvm_guest_init(void)
>>>>>>>>>  
>>>>>>>>>       paravirt_ops_setup();
>>>>>>>>>       register_reboot_notifier(&kvm_pv_reboot_nb);
>>>>>>>>> +     atomic_notifier_chain_register(&panic_notifier_list, 
>>>>>>>>> &kvm_pv_panic_nb);
>>>>>>>>>       for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++)
>>>>>>>>>               spin_lock_init(&async_pf_sleepers[i].lock);
>>>>>>>>>       if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF))
>>>>>>>>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>>>>>>>>> index 0b7690e..38b4705 100644
>>>>>>>>> --- a/arch/x86/kvm/svm.c
>>>>>>>>> +++ b/arch/x86/kvm/svm.c
>>>>>>>>> @@ -1900,10 +1900,14 @@ static int halt_interception(struct vcpu_svm 
>>>>>>>>> *svm)
>>>>>>>>>  
>>>>>>>>>  static int vmmcall_interception(struct vcpu_svm *svm)
>>>>>>>>>  {
>>>>>>>>> +     int ret;
>>>>>>>>> +
>>>>>>>>>       svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
>>>>>>>>>       skip_emulated_instruction(&svm->vcpu);
>>>>>>>>> -     kvm_emulate_hypercall(&svm->vcpu);
>>>>>>>>> -     return 1;
>>>>>>>>> +     ret = kvm_emulate_hypercall(&svm->vcpu);
>>>>>>>>> +
>>>>>>>>> +     /* Ignore the error? */
>>>>>>>>> +     return ret == 0 ? 0 : 1;
>>>>>>>>
>>>>>>>> Why can't kvm_emulate_hypercall return the right value?
>>>>>>>
>>>>>>> kvm_emulate_hypercall() will call kvm_hv_hypercall(), and
>>>>>>> kvm_hv_hypercall() will return 0 when vcpu's CPL > 0.
>>>>>>> If vcpu's CPL > 0, does kvm need to exit and tell it to
>>>>>>> qemu?
>>>>>>
>>>>>> No, there is currently no exit to userspace due to hypercalls, neither
>>>>>> of HV nor KVM kind.
>>>>>>
>>>>>> The point is that the return code of kvm_emulate_hypercall is unused so
>>>>>> far, so you can easily redefine it to encode continue vs. exit to
>>>>>> userspace. Once someone has different needs, this could still be
>>>>>> refactored again.
>>>>>
>>>>> So, it is OK to change the return value of kvm_hv_hypercall() if vcpu's
>>>>> CPL > 0?
>>>>
>>>> Yes, change it to encode what vendor modules need to return to their
>>>> callers.
>>>>
>>> Better introduce new request flag and set it in your hypercall emulation. 
>>> See
>>> how triple fault is handled.
>>
>> triple fault sets KVM_EXIT_SHUTDOWN and exits to userspace. Do you mean 
>> introduce
>> a new value(like KVM_EXIT_SHUTDOWN)?
>>
> I mean introduce new request bit (like KVM_REQ_TRIPLE_FAULT) and set it
> in your hypercall if exit to userspace is needed instead of changing
> return values.

I donot notice it. Thanks for you suggestion. I will modify my patch.

Thanks
Wen Congyang

> 
> --
>                       Gleb.
>