Re: [Qemu-devel] [PATCH v8] kvm: notify host when the guest is panicked

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Aug 08, 2012 at 10:43:01AM +0800, Wen Congyang wrote:
> We can know the guest is panicked when the guest runs on xen.
> But we do not have such feature on kvm.
> 
> Another purpose of this feature is: management app(for example:
> libvirt) can do auto dump when the guest is panicked. If management
> app does not do auto dump, the guest's user can do dump by hand if
> he sees the guest is panicked.
> 
> We have three solutions to implement this feature:
> 1. use vmcall
> 2. use I/O port
> 3. use virtio-serial.
> 
> We have decided to avoid touching hypervisor. The reason why I choose
> choose the I/O port is:
> 1. it is easier to implememt
> 2. it does not depend any virtual device
> 3. it can work when starting the kernel

How about searching for the "Kernel panic - not syncing" string 
in the guests serial output? Say libvirtd could take an action upon
that?

Advantages:
- It works for all architectures.
- It does not depend on any virtual device.
- It works as early as serial console output does (panics before
that should be rare).
- It allows you to see why the guest panicked.

> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
> ---
>  Documentation/virtual/kvm/pv_event.txt |   32 ++++++++++++++++++++++++++++++++
>  arch/ia64/include/asm/kvm_para.h       |   14 ++++++++++++++
>  arch/powerpc/include/asm/kvm_para.h    |   14 ++++++++++++++
>  arch/s390/include/asm/kvm_para.h       |   14 ++++++++++++++
>  arch/x86/include/asm/kvm_para.h        |   27 +++++++++++++++++++++++++++
>  arch/x86/kernel/kvm.c                  |   25 +++++++++++++++++++++++++
>  include/linux/kvm_para.h               |   23 +++++++++++++++++++++++
>  7 files changed, 149 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/virtual/kvm/pv_event.txt
> 
> diff --git a/Documentation/virtual/kvm/pv_event.txt b/Documentation/virtual/kvm/pv_event.txt
> new file mode 100644
> index 0000000..0ebc890
> --- /dev/null
> +++ b/Documentation/virtual/kvm/pv_event.txt
> @@ -0,0 +1,32 @@
> +The KVM paravirtual event interface
> +=================================
> +
> +Initializing the paravirtual event interface
> +======================
> +kvm_pv_event_init()
> +Argiments:
> +	None
> +
> +Return Value:
> +	0 : The guest kernel can't use paravirtual event interface.
> +	-1: The guest kernel can use paravirtual event interface.
> +
> +Querying whether the event can be ejected
> +======================
> +kvm_pv_has_feature()
> +Arguments:
> +	feature: The bit value of this paravirtual event to query
> +
> +Return Value:
> +	0: The guest kernel can't eject this paravirtual event.
> +	1: The guest kernel can eject this paravirtual event.
> +
> +
> +Ejecting paravirtual event
> +======================
> +kvm_pv_eject_event()
> +Arguments:
> +	event: The event to be ejected.
> +
> +Return Value:
> +	None
> diff --git a/arch/ia64/include/asm/kvm_para.h b/arch/ia64/include/asm/kvm_para.h
> index 2019cb9..b5ec658 100644
> --- a/arch/ia64/include/asm/kvm_para.h
> +++ b/arch/ia64/include/asm/kvm_para.h
> @@ -31,6 +31,20 @@ static inline bool kvm_check_and_clear_guest_paused(void)
>  	return false;
>  }
>  
> +static inline int kvm_arch_pv_event_init(void)
> +{
> +	return 0;
> +}
> +
> +static inline unsigned int kvm_arch_pv_features(void)
> +{
> +	return 0;
> +}
> +
> +static inline void kvm_arch_pv_eject_event(unsigned int event)
> +{
> +}
> +
>  #endif
>  
>  #endif
> diff --git a/arch/powerpc/include/asm/kvm_para.h b/arch/powerpc/include/asm/kvm_para.h
> index c18916b..01b98c7 100644
> --- a/arch/powerpc/include/asm/kvm_para.h
> +++ b/arch/powerpc/include/asm/kvm_para.h
> @@ -211,6 +211,20 @@ static inline bool kvm_check_and_clear_guest_paused(void)
>  	return false;
>  }
>  
> +static inline int kvm_arch_pv_event_init(void)
> +{
> +	return 0;
> +}
> +
> +static inline unsigned int kvm_arch_pv_features(void)
> +{
> +	return 0;
> +}
> +
> +static inline void kvm_arch_pv_eject_event(unsigned int event)
> +{
> +}
> +
>  #endif /* __KERNEL__ */
>  
>  #endif /* __POWERPC_KVM_PARA_H__ */
> diff --git a/arch/s390/include/asm/kvm_para.h b/arch/s390/include/asm/kvm_para.h
> index da44867..00ce058 100644
> --- a/arch/s390/include/asm/kvm_para.h
> +++ b/arch/s390/include/asm/kvm_para.h
> @@ -154,6 +154,20 @@ static inline bool kvm_check_and_clear_guest_paused(void)
>  	return false;
>  }
>  
> +static inline int kvm_arch_pv_event_init(void)
> +{
> +	return 0;
> +}
> +
> +static inline unsigned int kvm_arch_pv_features(void)
> +{
> +	return 0;
> +}
> +
> +static inline void kvm_arch_pv_eject_event(unsigned int event)
> +{
> +}
> +
>  #endif
>  
>  #endif /* __S390_KVM_PARA_H */
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 2f7712e..7d297f0 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -96,8 +96,11 @@ struct kvm_vcpu_pv_apf_data {
>  #define KVM_PV_EOI_ENABLED KVM_PV_EOI_MASK
>  #define KVM_PV_EOI_DISABLED 0x0
>  
> +#define KVM_PV_EVENT_PORT	(0x505UL)
> +
>  #ifdef __KERNEL__
>  #include <asm/processor.h>
> +#include <linux/ioport.h>
>  
>  extern void kvmclock_init(void);
>  extern int kvm_register_clock(char *txt);
> @@ -228,6 +231,30 @@ static inline void kvm_disable_steal_time(void)
>  }
>  #endif
>  
> +static inline int kvm_arch_pv_event_init(void)
> +{
> +	if (!request_region(KVM_PV_EVENT_PORT, 1, "KVM_PV_EVENT"))
> +		return -1;
> +
> +	return 0;
> +}
> +
> +static inline unsigned int kvm_arch_pv_features(void)
> +{
> +	unsigned int features = inl(KVM_PV_EVENT_PORT);
> +
> +	/* Reading from an invalid I/O port will return -1 */
> +	if (features == ~0)
> +		features = 0;
> +
> +	return features;
> +}
> +
> +static inline void kvm_arch_pv_eject_event(unsigned int event)
> +{
> +	outl(event, KVM_PV_EVENT_PORT);
> +}
> +
>  #endif /* __KERNEL__ */
>  
>  #endif /* _ASM_X86_KVM_PARA_H */
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index c1d61ee..6129459 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -368,6 +368,17 @@ 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_pv_eject_event(KVM_PV_EVENT_PANICKED);
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block kvm_pv_panic_nb = {
> +	.notifier_call = kvm_pv_panic_notify,
> +};
> +
>  static u64 kvm_steal_clock(int cpu)
>  {
>  	u64 steal;
> @@ -447,6 +458,20 @@ static void __init kvm_apf_trap_init(void)
>  	set_intr_gate(14, &async_page_fault);
>  }
>  
> +static void __init kvm_pv_panicked_event_init(void)
> +{
> +	if (!kvm_para_available())
> +		return;
> +
> +	if (kvm_pv_event_init())
> +		return;
> +
> +	if (kvm_pv_has_feature(KVM_PV_FEATURE_PANICKED))
> +		atomic_notifier_chain_register(&panic_notifier_list,
> +			&kvm_pv_panic_nb);
> +}
> +arch_initcall(kvm_pv_panicked_event_init);
> +
>  void __init kvm_guest_init(void)
>  {
>  	int i;
> diff --git a/include/linux/kvm_para.h b/include/linux/kvm_para.h
> index ff476dd..8e0fb81 100644
> --- a/include/linux/kvm_para.h
> +++ b/include/linux/kvm_para.h
> @@ -20,6 +20,12 @@
>  #define KVM_HC_FEATURES			3
>  #define KVM_HC_PPC_MAP_MAGIC_PAGE	4
>  
> +/* The bit of supported pv event */
> +#define KVM_PV_FEATURE_PANICKED	0
> +
> +/* The pv event value */
> +#define KVM_PV_EVENT_PANICKED	1
> +
>  /*
>   * hypercalls use architecture specific
>   */
> @@ -33,5 +39,22 @@ static inline int kvm_para_has_feature(unsigned int feature)
>  		return 1;
>  	return 0;
>  }
> +
> +static inline int kvm_pv_event_init(void)
> +{
> +	return kvm_arch_pv_event_init();
> +}
> +
> +static inline int kvm_pv_has_feature(unsigned int feature)
> +{
> +	if (kvm_arch_pv_features() & (1UL << feature))
> +		return 1;
> +	return 0;
> +}
> +
> +static inline void kvm_pv_eject_event(unsigned int event)
> +{
> +	kvm_arch_pv_eject_event(event);
> +}
>  #endif /* __KERNEL__ */
>  #endif /* __LINUX_KVM_PARA_H */
> -- 
> 1.7.1
> 
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