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RE: [Xen-users] GPLPV Network Driver causing VM crash

To: "Mark Pace" <pace@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-users] GPLPV Network Driver causing VM crash
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Sun, 1 Feb 2009 13:45:44 +1100
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Thread-topic: [Xen-users] GPLPV Network Driver causing VM crash
> 
> Sweet.  Thanks James.  That did the trick.
> 
> Would this 3.3.0 bug affect the Windows VMs regardless of the PV
drivers?
> 

I'm not sure. I have only heard of it being a problem when using my PV
drivers. There is a kernel call in Windows that preloads a certain
amount of data into the cache. This is a gross oversimplification, but
the routine in question runs like:

bytes_loaded = 0
while (bytes_loaded < bytes_to_load)
{
  ...
  bytes_loaded += cache_line_size
}

Because the cpuid isn't correct in 3.3.0 for AMD processors,
cache_line_size is always zero so bytes_loaded never increases and it
just spins forever.

NDIS (windows network stack) calls the above code when I give it a
packet and tell it that the checksum has already been calculated, but
that's the only time I have ever seen it called. It's a bit of a
mystery.

James

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