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

[Jan Kiszka <jan.kiszka@siemens.com>]

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.

Jan

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