Re: Userspace hypercalls?

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Dor Laor wrote:
>>
>> Thinking a little more about this, it isn't about handling hypercalls
>>     
> in
>   
>> userspace, but about handling a virtio sync() in userspace.
>>
>> So how about having a KVM_HC_WAKE_CHANNEL hypercall (similar to Xen's
>> event channel, but assymetric) that has a channel parameter.  The
>>     
> kernel
>   
>> handler for that hypercall dispatches calls to either a kernel handler
>> or a userspace handler.  That means we don't need a separate ETH_SEND,
>> ETH_RECEIVE, or BLOCK_SEND hypercalls.
>>
>>     
>
> Some points:
> - These were none receive/send/block_send hypercalls on the first place.
>   There were just register and notify hypercalls.
>   

But they were ethernet/block/whatever specific.  I'm proposing a single 
"wake this channel up" hypercall.

> - The balloon code also uses hypercalls and let userspace handle them so
>   higher layer will allow the guest inflate/deflate actions.
>   

That could be ported to virtio.  It is actually advantageous to balloon 
asynchronously.


-- 
Any sufficiently difficult bug is indistinguishable from a feature.


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