Re: [PATCH] kvm: notify host when guest paniced

[Wen Congyang]

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 <wency@xxxxxxxxxxxxxx>
>>>>>>> ---
>>>>>>>  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)?

Thanks
Wen Congyang

> 
> --
> 			Gleb.
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