linux-kernel - Re: [RFC PATCH 0/3] generic hypercall support

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Date:	Wed, 06 May 2009 12:03:27 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
CC:	Chris Wright <chrisw@...s-sol.org>,
	Gregory Haskins <gregory.haskins@...il.com>,
	Avi Kivity <avi@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] generic hypercall support

Anthony Liguori wrote:
> Gregory Haskins wrote:
>>
>> 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.
>>   
>
> PCI already provide a hypervisor agnostic interface (via IO regions). 
> You have a mechanism for devices to discover which regions they have
> allocated and to request remappings.  It's supported by Linux and
> Windows.  It works on the vast majority of architectures out there today.
>
> Why reinvent the wheel?

I suspect the current wheel is square.  And the air is out.  Plus its
pulling to the left when I accelerate, but to be fair that may be my
alignment....

:) But I digress.  See: http://patchwork.kernel.org/patch/21865/

To give PCI proper respect, I think its greatest value add here is the
inherent IRQ routing (which is a huge/difficult component, as I
experienced with dynirq in vbus v1).  Beyond that, however, I think we
can do better.

HTH
-Greg



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