Re: [PATCH] KVM: x86: Extend KVM_SET_VCPU_EVENTS with selective updates

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

Jan Kiszka wrote:
> User space may not want to overwrite asynchronously changing VCPU event
> states on write-back. So allow to skip nmi.pending and sipi_vector by
> setting corresponding bits in the flags field of kvm_vcpu_events.
> 

What will happen to this patch now? Merge during 2.6.33 window or drop?

Jan

> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> 
>  Documentation/kvm/api.txt  |   10 +++++++++-
>  arch/x86/include/asm/kvm.h |    4 ++++
>  arch/x86/kvm/x86.c         |    9 ++++++---
>  3 files changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
> index e1a1141..ee07e3a 100644
> --- a/Documentation/kvm/api.txt
> +++ b/Documentation/kvm/api.txt
> @@ -685,7 +685,7 @@ struct kvm_vcpu_events {
>  		__u8 pad;
>  	} nmi;
>  	__u32 sipi_vector;
> -	__u32 flags;   /* must be zero */
> +	__u32 flags;
>  };
>  
>  4.30 KVM_SET_VCPU_EVENTS
> @@ -701,6 +701,14 @@ vcpu.
>  
>  See KVM_GET_VCPU_EVENTS for the data structure.
>  
> +Fields that may be modified asynchronously by running VCPUs can be excluded
> +from the update. These fields are nmi.pending and sipi_vector. Set the
> +corresponding mask bits in the flags field to suppress overwriting their
> +current state:
> +
> +KVM_VCPUEVENT_MASK_NMI_PENDING - do not update nmi.pending
> +KVM_VCPUEVENT_MASK_SIPI_VECTOR - do not update sipi_vector
> +
>  
>  5. The kvm_run structure
>  
> diff --git a/arch/x86/include/asm/kvm.h b/arch/x86/include/asm/kvm.h
> index 950df43..acf8585 100644
> --- a/arch/x86/include/asm/kvm.h
> +++ b/arch/x86/include/asm/kvm.h
> @@ -254,6 +254,10 @@ struct kvm_reinject_control {
>  	__u8 reserved[31];
>  };
>  
> +/* When set in flags, skip corresponding fields on KVM_SET_VCPU_EVENTS */
> +#define KVM_VCPUEVENT_MASK_NMI_PENDING	0x00000001
> +#define KVM_VCPUEVENT_MASK_SIPI_VECTOR	0x00000002
> +
>  /* for KVM_GET/SET_VCPU_EVENTS */
>  struct kvm_vcpu_events {
>  	struct {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index dd15d7a..368843c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1953,7 +1953,8 @@ static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
>  static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
>  					      struct kvm_vcpu_events *events)
>  {
> -	if (events->flags)
> +	if (events->flags &
> +	    ~(KVM_VCPUEVENT_MASK_NMI_PENDING | KVM_VCPUEVENT_MASK_SIPI_VECTOR))
>  		return -EINVAL;
>  
>  	vcpu_load(vcpu);
> @@ -1970,10 +1971,12 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
>  		kvm_pic_clear_isr_ack(vcpu->kvm);
>  
>  	vcpu->arch.nmi_injected = events->nmi.injected;
> -	vcpu->arch.nmi_pending = events->nmi.pending;
> +	if (!(events->flags & KVM_VCPUEVENT_MASK_NMI_PENDING))
> +		vcpu->arch.nmi_pending = events->nmi.pending;
>  	kvm_x86_ops->set_nmi_mask(vcpu, events->nmi.masked);
>  
> -	vcpu->arch.sipi_vector = events->sipi_vector;
> +	if (!(events->flags & KVM_VCPUEVENT_MASK_SIPI_VECTOR))
> +		vcpu->arch.sipi_vector = events->sipi_vector;
>  
>  	vcpu_put(vcpu);
>  
> 

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