Re: PCI passthrough resource remapping

[Avi Kivity <avi@redhat.com>]

On 01/14/2010 08:31 PM, Ryan C. Underwood wrote:
>
> On Thu, Jan 14, 2010 at 05:54:51PM +0200, Avi Kivity wrote:
>    
>> On 01/14/2010 05:47 PM, Michael S. Tsirkin wrote:
>>      
>>>        
>>>> Michael, I think 'DisINTx-' means the device is not PCI 2.3 compliant?
>>>>          
>>> No it doesn't, just that interrupt disable bit is not set.
>>>        
>> Thanks.  Ryan, while kvm doesn't support assigning a device with
>> shared interrupts now, in the future it will likely be possible to
>> share it.  You'll still need an iommu.
>>      
> No IOMMU on this machine and this is all integrated hardware.
>
> This IOMMU requirement seems so strange.  I used to pass through PCI
> devices ages ago when using the DOSEMU emulator.  It emulated PCI BIOS
> functions and mapped the PCI config space and memory regions into the
> emulator process.  The device interrupt was grabbed and handled in the
> emulator's kernel support, waking up the emulator when an interrupt came
> in.
>
> I don't really know anything about kvm internals, but I'd like to
> understand more about the particulars of the IOMMU requirement if you
> don't mind.
>    

PCI cards can access system memory directly.  If you assign a card to a 
guest, the guest will program the card to transfer data to system memory 
using guest addresses; since guest addresses don't correspond to host 
addresses, memory corruption will ensue.

Not sure about your experience with DOSEMU; maybe these devices were not 
dma capable.

-- 
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signature is too narrow to contain.