linux-kernel - Re: iommu_intel or i915 regression in 4.18, 4.19.12 and drm-tip

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

Message-ID: <154659116310.4596.13613897418163029789@jlahtine-desk.ger.corp.intel.com>
Date:   Fri, 04 Jan 2019 10:39:23 +0200
From:   Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
To:     Eric Wong <e@...24.org>
Cc:     Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...ux.ie>,
        David Woodhouse <dwmw2@...radead.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        iommu@...ts.linux-foundation.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: iommu_intel or i915 regression in 4.18, 4.19.12 and drm-tip

Quoting Eric Wong (2019-01-04 03:06:26)
> Joonas Lahtinen <joonas.lahtinen@...ux.intel.com> wrote:
> > Quoting Eric Wong (2018-12-27 13:49:48)
> > > I just got a used Thinkpad X201 (Core i5 M 520, Intel QM57
> > > chipset) and hit some kernel panics while trying to view
> > > image/animation-intensive stuff in Firefox (X11) unless I use
> > > "iommu_intel=igfx_off".
> > > 
> > > With Debian stable backport kernels, "linux-image-4.17.0-0.bpo.3-amd64"
> > > (4.17.17-1~bpo9+1) has no problems.  But "linux-image-4.18.0-0.bpo.3-amd64"
> > > (4.18.20-2~bpo9+1) gives a blank screen before I can login via agetty
> > > and run startx.
> 
> > Most confusing about this is that 4.17 would have worked to begin with,
> > without intel_iommu=igfx_off (unless it was the default for older
> > kernel?)
> 
> Yeah, so the Debian bpo 4.17(.17) kernel did not set
> CONFIG_INTEL_IOMMU_DEFAULT_ON, so I didn't encounter problems.
> My self-built kernels all set CONFIG_INTEL_IOMMU_DEFAULT_ON.

So it's the case that IOMMU never worked on your machine.

My recommendation would be to simply use intel_iommu=igfx_off if you
need IOMMU.

Old hardware is known to have issues with IOMMU, and retroactively
enabling IOMMU on those machines just brings them up :/

Regards, Joonas

> Booting the Debian 4.17 kernel with "intel_iommu=on" gives the
> same hanging problem I hit with self-built 4.19.{12,13} kernels.
> 
> I'm not sure how far back the problem goes (maybe forever),
> since I only got this hardware.  Not sure what's the problem
> with Debian 4.18, either; but (self-built) 4.19.13 is fine w/o
> CONFIG_INTEL_IOMMU_DEFAULT_ON.
> 
> Debian backports doesn't have kernels for 4.19 or 4.20, yet.
> 
> > Did you maybe update other parts of the system while updating the
> > kernel?
> 
> Definitely not; just the kernel + headers ("make bindeb-pkg)".
> 
> > If you could attach full boot dmesg from working and non-working kernel +
> > have config file of both kernel's in Bugzilla. That'd be a good start!
> 
> Sorry, I get anxiety attacks when it comes to logins and forms.
> Anyways, I managed to get the Debian kernel dmesg output uploaded
> with and without iommu_intel=on:
> https://bugs.freedesktop.org/attachment.cgi?bugid=109219