linux-kernel - Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

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Date:	Mon, 10 Nov 2008 22:08:45 -0800
From:	Greg KH <greg@...ah.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	"Fischer, Anna" <anna.fischer@...com>, H L <swdevyid@...oo.com>,
	"randy.dunlap@...cle.com" <randy.dunlap@...cle.com>,
	"grundler@...isc-linux.org" <grundler@...isc-linux.org>,
	"Chiang, Alexander" <achiang@...com>,
	"matthew@....cx" <matthew@....cx>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"rdreier@...co.com" <rdreier@...co.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>
Subject: Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

On Sun, Nov 09, 2008 at 09:37:20PM +0200, Avi Kivity wrote:
> Greg KH wrote:
>> On Sun, Nov 09, 2008 at 02:44:06PM +0200, Avi Kivity wrote:
>>   
>>> Greg KH wrote:
>>>     
>>>> It's that "second" part that I'm worried about.  How is that going to
>>>> happen?  Do you have any patches that show this kind of "assignment"?
>>>>
>>>>         
>>> For kvm, this is in 2.6.28-rc.
>>>     
>>
>> Where?  I just looked and couldn't find anything, but odds are I was
>> looking in the wrong place :(
>>
>>   
>
> arch/x86/kvm/vtd.c: iommu integration (allows assigning the device's memory 
> resources)

That file is not in 2.6.28-rc4 :(


> virt/kvm/irq*: interrupt redirection (allows assigning the device's 
> interrupt resources)

I only see virt/kvm/irq_comm.c in 2.6.28-rc4.

> the rest (pci config space, pio redirection) are in userspace.

So you don't need these pci core changes at all?

>>> Note there are two ways to assign a device to a guest:
>>>
>>> - run the VF driver in the guest: this has the advantage of best 
>>> performance, but requires pinning all guest memory, makes live migration 
>>> a tricky proposition, and ties the guest to the underlying hardware.
>>
>> Is this what you would prefer for kvm?
>>
>
> It's not my personal preference, but it is a supported configuration.  For 
> some use cases it is the only one that makes sense.
>
> Again, VF-in-guest and VF-in-host both have their places.  And since Linux 
> can be both guest and host, it's best if the VF driver knows nothing about 
> SR-IOV; it's just a pci driver.  The PF driver should emulate anything that 
> SR-IOV does not provide (like missing pci config space).

Yes, we need both.

thanks,

greg k-h
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