Re: [PATCH 5/9] KVM: Adds ability to signal userspace using a file-descriptor

[Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

This patch series depends on eventfd which means that KVM now requires 
2.6.22-rc1.

While KVM will inevitably start requiring newer kernel versions, do we 
really need to do it right now?  Perhaps we could add dummy eventfd_* 
functions to the module compat header?  Then at least older kernels will 
continue to work with in-kernel APIC disabled.

Regards,

Anthony Liguori

Gregory Haskins wrote:
> Signed-off-by: Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org>
> ---
>
>  drivers/kvm/kvm.h      |    1 +
>  drivers/kvm/kvm_main.c |   55 +++++++++++++++++++++++++++++++++++++++++++-----
>  include/linux/kvm.h    |    1 +
>  3 files changed, 51 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
> index d5783dc..e1ba066 100644
> --- a/drivers/kvm/kvm.h
> +++ b/drivers/kvm/kvm.h
> @@ -332,6 +332,7 @@ struct kvm_vcpu_irq {
>  	int                  pending;
>  	int                  deferred;
>  	int                  guest_cpu;
> +	int                  eventfd;
>  };
>  
>  struct kvm_vcpu {
> diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
> index 0c6a62a..7109b66 100644
> --- a/drivers/kvm/kvm_main.c
> +++ b/drivers/kvm/kvm_main.c
> @@ -40,6 +40,7 @@
>  #include <linux/file.h>
>  #include <linux/fs.h>
>  #include <linux/mount.h>
> +#include <linux/eventfd.h>
>  
>  #include "x86_emulate.h"
>  #include "segment_descriptor.h"
> @@ -326,6 +327,7 @@ static struct kvm *kvm_create_vm(void)
>  		memset(&vcpu->irq, 0, sizeof(vcpu->irq));
>  		spin_lock_init(&vcpu->irq.lock);
>  		vcpu->irq.deferred = -1;
> +		vcpu->irq.eventfd   = -1;
>  
>  		vcpu->cpu = -1;
>  		vcpu->kvm = kvm;
> @@ -2358,6 +2360,7 @@ static void kvm_vcpu_intr(struct kvm_irqsink *this,
>  {
>  	struct kvm_vcpu *vcpu = (struct kvm_vcpu*)this->private;
>  	int direct_ipi = -1;
> +	int eventfd = -1;
>  
>  	spin_lock_irq(&vcpu->irq.lock);
>  
> @@ -2379,7 +2382,14 @@ static void kvm_vcpu_intr(struct kvm_irqsink *this,
>  				 */
>  				direct_ipi = vcpu->irq.guest_cpu;
>  				BUG_ON(direct_ipi == smp_processor_id());
> -			}
> +			} else
> +				/*
> +				 * otherwise, we must assume that we could be
> +				 * blocked anywhere, including userspace. Send
> +				 * a signal to give everyone a chance to get
> +				 * notification
> +				 */
> +				eventfd = vcpu->irq.eventfd;
>  		}
>  	}
>  
> @@ -2401,6 +2411,12 @@ static void kvm_vcpu_intr(struct kvm_irqsink *this,
>  		smp_call_function_single(direct_ipi,
>  					 kvm_vcpu_guest_intr,
>  					 vcpu, 0, 0);
> +
> +	if (eventfd != -1) {
> +		struct file *filp = eventfd_fget(eventfd);
> +		if (!IS_ERR(filp))
> +			eventfd_signal(filp, 1);
> +	}
>  }
>  
>  static void kvm_vcpu_irqsink_init(struct kvm_vcpu *vcpu)
> @@ -2584,6 +2600,17 @@ static int kvm_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
>  	return 0;
>  }
>  
> +static int kvm_vcpu_ioctl_set_eventfd(struct kvm_vcpu *vcpu, int fd)
> +{
> +	if (IS_ERR(eventfd_fget(fd)))
> +		return -EINVAL;
> +
> +	vcpu->irq.eventfd = fd;
> +	smp_wmb();
> +
> +	return 0;
> +}
> +
>  static long kvm_vcpu_ioctl(struct file *filp,
>  			   unsigned int ioctl, unsigned long arg)
>  {
> @@ -2753,6 +2780,15 @@ static long kvm_vcpu_ioctl(struct file *filp,
>  		r = 0;
>  		break;
>  	}
> +	case KVM_SET_EVENTFD: {
> +		int eventfd = (long)argp;
> +
> +		r = kvm_vcpu_ioctl_set_eventfd(vcpu, eventfd);
> +		if (r)
> +			goto out;
> +		r = 0;
> +		break;
> +	}
>  	default:
>  		;
>  	}
> @@ -2937,12 +2973,19 @@ static long kvm_dev_ioctl(struct file *filp,
>  		r = 0;
>  		break;
>  	}
> -	case KVM_CHECK_EXTENSION:
> -		/*
> -		 * No extensions defined at present.
> -		 */
> -		r = 0;
> +	case KVM_CHECK_EXTENSION: {
> +		int ext = (long)argp;
> +
> +		switch (ext) {
> +		case KVM_SET_EVENTFD:
> +			r = 1;
> +			break;
> +		default:
> +			r = 0;
> +			break;
> +		}
>  		break;
> +	}
>  	case KVM_GET_VCPU_MMAP_SIZE:
>  		r = -EINVAL;
>  		if (arg)
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> index e6edca8..f13ec8c 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -300,5 +300,6 @@ struct kvm_signal_mask {
>  #define KVM_SET_SIGNAL_MASK       _IOW(KVMIO,  0x8b, struct kvm_signal_mask)
>  #define KVM_GET_FPU               _IOR(KVMIO,  0x8c, struct kvm_fpu)
>  #define KVM_SET_FPU               _IOW(KVMIO,  0x8d, struct kvm_fpu)
> +#define KVM_SET_EVENTFD           _IO(KVMIO,   0x8e)
>  
>  #endif
>
>
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