[Beowulf] RHEL7 kernel update for L1TF vulnerability breaks RDMA

Peter St. John peter.st.john at gmail.com
Mon Sep 10 08:25:55 PDT 2018

I had wanted to say that such a bug would be caught by compiling with some
reasonalbe warning level; but I think I was wrong.

I compiled

with some wrapper and got nothing with whatever gcc I have on this laptop,
gcc -Wextra

which is more persnickety than -Wall, and just got
mynoop.c: In function 'main':
mynoop.c:4:10: warning: suggest braces around empty body in an 'if'
statement [-Wempty-body]

So I guess I have to forgive the software engineer who fat-fingered that
semicolon. Of course I've done worse.


On Mon, Sep 10, 2018 at 4:22 AM, Chris Samuel <chris at csamuel.org> wrote:

> On Friday, 17 August 2018 2:47:37 PM AEST Chris Samuel wrote:
> > Just a heads up that the 3.10.0-862.11.6.el7.x86_64 kernel from
> > that was released to address the most recent Intel CPU problem "L1TF"
> seems
> > to break RDMA (found by a colleague here at Swinburne).
> So this CentOS bug has a one line bug fix for this problem!
> https://bugs.centos.org/view.php?id=15193
> It's a corker - basically it looks like someone typo'd a ; into an if
> statement, the fix is:
> -       if (!rdma_is_port_valid_nospec(device, &ah_attr->port_num));
> +       if (!rdma_is_port_valid_nospec(device, &ah_attr->port_num))
>                 return -EINVAL;
> So it always returns -EINVAL when checking the port as the if becomes a
> noop..
> :-(
> Patch attached...
> --
>  Chris Samuel  :  http://www.csamuel.org/  :  Melbourne, VIC
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