Re: [PATCH 6/6 V2] Add age out of guest paused flag

[Anthony Liguori <aliguori@us.ibm.com>]

On 10/31/2011 03:07 PM, Eric B Munson wrote:
> The KVM_GUEST_PAUSED flag will prevent a guest from compaining about a soft
> lockup but it can mask real soft lockups if the flag isn't cleared when it is
> no longer relevant.  This patch adds a kvm ioctl that the hypervisor will use
> when it resumes a guest to start a timer for aging out the flag.  The time out
> will be specified by the hypervisor in the ioctl call.
>
> Signed-off-by: Eric B Munson<emunson@mgebm.net>

Why not have the guest clear the flag when it acknowledges it?

The hypervisor would unconditionally set the bit, and the guest would do a 
testandclear to check if the bit is set.  I think that avoids the whole aging 
business.

Regards,

Anthony Liguori

> ---
> Cahnges from V1:
>   Add host functions for flag management to arch/x86/kvm/x86.c instead of
> kvmclock.c
>
>   arch/x86/include/asm/pvclock.h |    2 ++
>   arch/x86/kvm/x86.c             |   32 ++++++++++++++++++++++++++++++++
>   include/linux/kvm.h            |    2 ++
>   include/linux/kvm_host.h       |    2 ++
>   4 files changed, 38 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
> index 9312814..e8460b9 100644
> --- a/arch/x86/include/asm/pvclock.h
> +++ b/arch/x86/include/asm/pvclock.h
> @@ -18,6 +18,8 @@ void kvm_set_host_stopped(struct kvm_vcpu *vcpu);
>
>   bool kvm_check_and_clear_host_stopped(int cpu);
>
> +void kvm_clear_guest_paused(struct kvm_vcpu *vcpu, unsigned int length);
> +
>   /*
>    * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
>    * yielding a 64-bit result.
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 592ac3b..fb0132a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -46,6 +46,7 @@
>   #include<linux/hash.h>
>   #include<linux/pci.h>
>   #include<trace/events/kvm.h>
> +#include<linux/timer.h>
>
>   #define CREATE_TRACE_POINTS
>   #include "trace.h"
> @@ -3300,6 +3301,15 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>   		kvm_set_host_stopped(vcpu);
>   		break;
>   	}
> +	case KVM_CLEAR_GUEST_PAUSED: {
> +		unsigned int length;
> +		r = -EFAULT;
> +		if (copy_from_user(&length, argp, sizeof length))
> +			goto out;
> +		r = 0;
> +		kvm_clear_guest_paused(vcpu, length);
> +		break;
> +	}
>   	default:
>   		r = -EINVAL;
>   	}
> @@ -6133,6 +6143,28 @@ void kvm_set_host_stopped(struct kvm_vcpu *vcpu)
>   }
>   EXPORT_SYMBOL_GPL(kvm_set_host_stopped);
>
> +static void kvm_timer_clear_guest_paused(unsigned long vcpu_addr)
> +{
> +	struct kvm_vcpu *vcpu = (struct kvm_vcpu *)vcpu_addr;
> +	struct pvclock_vcpu_time_info *src =&vcpu->arch.hv_clock;
> +	src->flags = src->flags&  (~PVCLOCK_GUEST_STOPPED);
> +}
> +
> +/*
> + * Host has resumed the guest, we need to clear the guest paused flag so we
> + * don't mask any real soft lockups.
> + */
> +void kvm_clear_guest_paused(struct kvm_vcpu *vcpu, unsigned int length)
> +{
> +	if (!timer_pending(&vcpu->flag_timer))
> +		setup_timer(&vcpu->flag_timer,
> +			    kvm_timer_clear_guest_paused,
> +			    (unsigned long)vcpu);
> +	mod_timer(&vcpu->flag_timer,
> +		  jiffies + (length * HZ));
> +}
> +EXPORT_SYMBOL_GPL(kvm_clear_guest_paused);
> +
>   int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
>   				  struct kvm_sregs *sregs)
>   {
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index 87cab0d..bd9724c 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -765,6 +765,8 @@ struct kvm_clock_data {
>   #define KVM_ALLOCATE_RMA	  _IOR(KVMIO,  0xa9, struct kvm_allocate_rma)
>   /* VM is being stopped by host */
>   #define KVM_GUEST_PAUSED	  _IO(KVMIO,   0xaa)
> +/* Start the timer to clear the paused flag */
> +#define KVM_CLEAR_GUEST_PAUSED	  _IO(KVMIO,   0xab)
>
>   #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1<<  0)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index d526231..043af4d 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -19,6 +19,7 @@
>   #include<linux/slab.h>
>   #include<linux/rcupdate.h>
>   #include<linux/ratelimit.h>
> +#include<linux/timer.h>
>   #include<asm/signal.h>
>
>   #include<linux/kvm.h>
> @@ -154,6 +155,7 @@ struct kvm_vcpu {
>   #endif
>
>   	struct kvm_vcpu_arch arch;
> +	struct timer_list flag_timer;
>   };
>
>   static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)