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SubjectRe: [RFC PATCH 0/3] generic hypercall support
Chris Wright wrote:
> * Gregory Haskins (ghaskins@novell.com) wrote:
>
>> Chris Wright wrote:
>>
>>> But a free-form hypercall(unsigned long nr, unsigned long *args, size_t count)
>>> means hypercall number and arg list must be the same in order for code
>>> to call hypercall() in a hypervisor agnostic way.
>>>
>> Yes, and that is exactly the intention. I think its perhaps the point
>> you are missing.
>>
>
> Yes, I was reading this as purely any hypercall, but it seems a bit
> more like:
> pv_io_ops->iomap()
> pv_io_ops->ioread()
> pv_io_ops->iowrite()
>

Right.

> <snip>
>
>> Today, there is no equivelent of a platform agnostic "iowrite32()" for
>> hypercalls so the driver would look like the pseudocode above except
>> substitute with kvm_hypercall(), lguest_hypercall(), etc. The proposal
>> is to allow the hypervisor to assign a dynamic vector to resources in
>> the backend and convey this vector to the guest (such as in PCI
>> config-space as mentioned in my example use-case). The provides the
>> "address negotiation" function that would normally be done for something
>> like a pio port-address. The hypervisor agnostic driver can then use
>> this globally recognized address-token coupled with other device-private
>> ABI parameters to communicate with the device. This can all occur
>> without the core hypervisor needing to understand the details beyond the
>> addressing.
>>
>
> VF drivers can also have this issue (and typically use mmio).
> I at least have a better idea what your proposal is, thanks for
> explanation. Are you able to demonstrate concrete benefit with it yet
> (improved latency numbers for example)?
>

I had a test-harness/numbers for this kind of thing, but its a bit
crufty since its from ~1.5 years ago. I will dig it up, update it, and
generate/post new numbers.

Thanks Chris,
-Greg


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