Re: [PATCH 13/15] KVM: Add support for enabling capabilities per-vcpu

[Avi Kivity <avi@redhat.com>]

On 03/08/2010 08:03 PM, Alexander Graf wrote:
> Some times we don't want all capabilities to be available to all
> our vcpus. One example for that is the OSI interface, implemented
> in the next patch.
>
> In order to have a generic mechanism in how to enable capabilities
> individually, this patch introduces a new ioctl that can be used
> for this purpose. That way features we don't want in all guests or
> userspace configurations can just not be enabled and we're good.
>
>
> diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
> index d170cb4..6a19ab6 100644
> --- a/Documentation/kvm/api.txt
> +++ b/Documentation/kvm/api.txt
> @@ -749,6 +749,21 @@ Writes debug registers into the vcpu.
>   See KVM_GET_DEBUGREGS for the data structure. The flags field is unused
>   yet and must be cleared on entry.
>
> +4.34 KVM_ENABLE_CAP
> +
> +Capability: basic
>    

Capability: basic means that the feature was present in 2.6.22.  
Otherwise you need to specify the KVM_CAP_ that presents this feature.

> +Architectures: all
>
>    

But it's implemented for ppc only (other arches will get ENOTTY).

> +Not all extensions are enabled by default. Using this ioctl the application
> +can enable an extension, making it available to the guest.
> +
> +On systems that do not support this ioctl, it always fails. On systems that
> +do support it, it only works for extensions that are supported for enablement.
> +As of writing this the only enablement enabled extenion is KVM_CAP_PPC_OSI.
>    

That needs to be documented.  It also needs to be discoverable 
separately - we can have a kernel with KVM_ENABLE_CAP but without 
KVM_CAP_PPC_OSI.

btw, KVM_CAP_PPC_OSI conflicts with the KVM_CAP_ namespace.  Please 
choose another namespace.

Need to document the structure fields.

>
>   /*
> @@ -696,6 +705,8 @@ struct kvm_clock_data {
>   /* Available with KVM_CAP_DEBUGREGS */
>   #define KVM_GET_DEBUGREGS         _IOR(KVMIO,  0xa1, struct kvm_debugregs)
>   #define KVM_SET_DEBUGREGS         _IOW(KVMIO,  0xa2, struct kvm_debugregs)
> +/* No need for CAP, because then it just always fails */
> +#define KVM_ENABLE_CAP            _IOW(KVMIO,  0xa3, struct kvm_enable_cap)
>    
The CAPs are needed so you can discover what you have without running guests.



-- 
error compiling committee.c: too many arguments to function