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

[Wen Congyang <wency@cn.fujitsu.com>]

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@cn.fujitsu.com>
>>>> ---
>>>>  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?

Thanks
Wen Congyang
> 
> Jan
>