Subject: BUG: Mellanox crash with iommu=soft and swiotlb=force

From: Christoffer Dall <[email-masked]>
Date: Mon, 28 Sep 2015 23:04:50 +0200

Hi,

In doing some performance experiments I found that using a 10G Mellanox
MX354A Dual port FDR CX3 device on a server running Apache and running
ab against that server causes the system to crash with 'iommu=soft
swiotlb=force'.  The same behavior is seen without these options on Dom0
running under Xen.

I have tried this on v4.0 and v4.3-rc3.

Examples of crashes:
http://pastebin.ubuntu.com/11953498/
http://pastebin.ubuntu.com/11953443/

Kernel config (v4.3):
http://paste.ubuntu.com/12605446/

To reproduce, host a file in apache server on a system with the Mellanox
NIC (I used the 41K index file of the GCC manual) and run ab (apache
bench) from a client machine, something like this:

$ ab -n 100000 -c 100 http://10.10.1.2/gcc/index.html

I'm afraid debugging this is out of my area of expertise.  Is this
something you could have a look at?

Thanks,
-Christoffer