Re: [Xen-devel] Oops when modprobing ivtv outside of dom0

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 5 Jul 2005, at 22:28, David Muench wrote:

> I just tried a second time, and it took a few tries of capturing video
> to crash it. But even when it didn't crash, all I got was a zero byte
> file. I noticed the card was using interrupts (looking at
> /proc/interrupts), and things looked ok in dmesg, but no mpeg data.
> That time the domU didn't exit on it's own, but was pretty well hung
> up (non-responsive other than line feeds on the console). So I tried
> to xm destroy it, and that rebooted the entire box.
I think the ivtv driver is probably not calculating dma addresses in 
the way that xen requires. On native Linux, if you allocate a 
multi-page chunk of physical memory, you can pass the start address of 
that buffer to hardware and it can dma the entire buffer given just 
that address. In Xen, because we give guests 'pseudo-physical' memory, 
that physical buffer may not be really physically contiguous. So we 
need drivers to dma_alloc_coherent or pci_alloc_consistent the memory 
they will use for dma --- we modified those functions to ensure they 
return suitable contiguous physical memory.
Perhaps the developers may know where to look further.

 -- Keir


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