linux-kernel - Please stop using iopl() in DPDK

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrVepdYd4uN8jrG8i6iaixWp+N3MdGv5WhjOdCr9sLRK1w@mail.gmail.com>
Date:   Thu, 24 Oct 2019 21:45:56 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     dev@...k.org, Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Please stop using iopl() in DPDK

Hi all-

Supporting iopl() in the Linux kernel is becoming a maintainability
problem.  As far as I know, DPDK is the only major modern user of
iopl().

After doing some research, DPDK uses direct io port access for only a
single purpose: accessing legacy virtio configuration structures.
These structures are mapped in IO space in BAR 0 on legacy virtio
devices.

There are at least three ways you could avoid using iopl().  Here they
are in rough order of quality in my opinion:

1. Change pci_uio_ioport_read() and pci_uio_ioport_write() to use
read() and write() on resource0 in sysfs.

2. Use the alternative access mechanism in the virtio legacy spec:
there is a way to access all of these structures via configuration
space.

3. Use ioperm() instead of iopl().

We are considering changes to the kernel that will potentially harm
the performance of any program that uses iopl(3) -- in particular,
context switches will become more expensive, and the scheduler might
need to explicitly penalize such programs to ensure fairness.  Using
ioperm() already hurts performance, and the proposed changes to iopl()
will make it even worse.  Alternatively, the kernel could drop iopl()
support entirely.  I will certainly make a change to allow
distributions to remove iopl() support entirely from their kernels,
and I expect that distributions will do this.

Please fix DPDK.

Thanks,
Andy