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

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Message-ID: <49173BF0.5050506@redhat.com>
Date:	Sun, 09 Nov 2008 21:37:20 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Greg KH <greg@...ah.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

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

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

>> 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).

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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