Created attachment 341029 [details]
upstream backport of iwlwifi-fix-TX-cmd-dma-unmapping.patch to 5.4

Description of problem:
When enabling the Intel VT-d support on a Dell E6500 with an Intel 5100
wireless device, the system will crash when it tries to configure
the wireless.

Version-Release number of selected component (if applicable):


How reproducible:
Every time on boot if:
An Intel system with VT-d support, and a RHEL5.4 kernel with VT-d support included & enabled(intel_iommu=on), and an Intel 5100 wireless is enabled to
be configured.

Steps to Reproduce:
Can also do this:
1. blacklist iwlagn in /etc/modprobe.conf
2. bring up aforementioned hw & kernel
3. modprobe iwlagn
4. iwconfig wlan0 essid <local wireless pt>
5. dhclient wlan0
    ^-- crashes here
  
Actual results:
Crashes.

Expected results:
System continues to operate.
Wireless configures successfully.

Additional info:
(1) Took the rhel5.4-140 iwl driver and added the posted patches for
BZ 474699 (address problems switching btwn WPA & WEP) because it
had RX skb alignment fixes -- still crashed with this patch.
(2) backported the following upstream commit to the iwl driver:
    499b1883038a7db2dcf8b64229f8533ce2c8f0fc
(will attach the backported version for review).
 -- This stopped the iwl from crashing the kernel,
     but the iwl wouldn't successfully configure either;
     so, not sure if it cured one problem, created another,
     or just avoided the original iwl DMA mapping problem.
(3) this type of DMA mapping error has been seen in other
    upstream drivers when Intel Vt-d was enabled, and DMA 
    mapping bugs show up once real IOMMUs are
    in the hw path. 
     Typically, the driver error is due to multiple dma-like free/unmaps,
     improper params' passed to dma_[un]map_single(), etc.

Although laptops are not a primary target for RHEL5.4+KVM+VTd,
the chip set used in them is common in other laptops (Thinkpad x200,
Dell E6400, etc.), and are used by numerous KVM & VTD developers
as test machines (due to portability, costs, etc.).
Several patches to the VT-d code have been made to accomodate these
machines, or the drivers they use, in order to keep this set of 
developers 'healthy'.  To encourage RHEL5.4 use, a fix for the RHEL5.4
iwlwifi driver would be prudent.