linux-kernel - Re: [PATCH] kvm: notify host when guest paniced

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Date:	Tue, 28 Feb 2012 12:45:28 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
Cc:	Wen Congyang <wency@...fujitsu.com>,
	kvm list <kvm@...r.kernel.org>, Avi Kivity <avi@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Daniel P. Berrange" <berrange@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>
Subject: Re: [PATCH] kvm: notify host when guest paniced

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@...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?
> 
> 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.

--
			Gleb.
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