RE: [Xen-users] Xen 3.0.0 32bit-pae (testing changeset 8270) crashes(pgtable.c:284, kernel bug?)

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Matt Ayres
> Sent: 02 February 2006 16:06
> To: Ian Pratt
> Cc: Keir Fraser; ian.pratt@xxxxxxxxxxxx; Ralph Passgang; 
> xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Xen 3.0.0 32bit-pae (testing 
> changeset 8270) crashes(pgtable.c:284, kernel bug?)
> 
> Ian,
> 
> I'll buy that the 3w-xxxx driver sucks and it's best to have 
> a controller than that can do DMA above 4GB.  The problem is 
> the 3w-xxxx series has been one of the best RAID controllers 
> on the market for the past few years and many, many people 
> have them.  
> Even if it's through a bunch hacks, hardware that can't do 
> DMA above 4GB needs to work reliably.  This is crucial for 
> Xen to be "Enterprise-Grade Open Source Virtualization". 
> 
> (just a casual observation from someone who spends day in and 
> day out working with Xen)

This is why Mark Langsdorf (and probably others) have been working on an
IOMMU driver for Xen, to at least support AMD64 solutions for this type
of problem [unfortunately, the AMD IOMMU solution doesn't work on Intel
machines due to different hardware architecture :-( ]. 

And it's not just 3Ware that has this problem. Many, many PCI
DMA-engines are not designed to access memory above 4GB. I'd say almost
all DMA cards that haven't had the actual PCI interface redesigned in
the last two years or so, with a few exceptions on high-end SCSI and
Ethernet controllers, would have a 32-bit limit for it's physical
address. The PCI spec supports both 32- and 64-bit addressing, but it's
optional for the chip designer to implement more than 32 bits of
addressing.

--
Mats
> 
> Thank you,
> Matt Ayres
> > There's all manner of crappy hardware that can't do DMA 
> above 4GB. The 
> > other problem that caused you to upgrade to 3.0.1 was 3ware 
> specific, 
> > a workaround for the driver being lazy.
> >
> > I believe some newer 3ware controllers are capable of DMA 
> above 4GB, 
> > though I don't know specific model numbers. 3ware tech support are 
> > actually pretty responsive, so I'm sure they can help you.
> >
> >   
> 
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> 
> 


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