From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jason Andryuk <jandryuk@gmail.com>
Cc: Jan Beulich <jbeulich@suse.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
<intel-gfx@lists.freedesktop.org>,
xen-devel <xen-devel@lists.xenproject.org>,
eric chanudet <eric.chanudet@gmail.com>
Subject: Re: i915 dma faults on Xen
Date: Mon, 22 Feb 2021 11:18:07 +0100 [thread overview]
Message-ID: <YDOE35zhQYwgaxke@Air-de-Roger> (raw)
In-Reply-To: <CAKf6xpuTbvGtTRHPK9Ock7rxJk4DfCumgTW7-2_PADm9cSaUBg@mail.gmail.com>
On Fri, Feb 19, 2021 at 12:30:23PM -0500, Jason Andryuk wrote:
> On Wed, Oct 21, 2020 at 9:59 AM Jan Beulich <jbeulich@suse.com> wrote:
> >
> > On 21.10.2020 15:36, Jason Andryuk wrote:
> > > On Wed, Oct 21, 2020 at 8:53 AM Jan Beulich <jbeulich@suse.com> wrote:
> > >>
> > >> On 21.10.2020 14:45, Jason Andryuk wrote:
> > >>> On Wed, Oct 21, 2020 at 5:58 AM Roger Pau Monné <roger.pau@citrix.com> wrote:
> > >>>> Hm, it's hard to tell what's going on. My limited experience with
> > >>>> IOMMU faults on broken systems there's a small range that initially
> > >>>> triggers those, and then the device goes wonky and starts accessing a
> > >>>> whole load of invalid addresses.
> > >>>>
> > >>>> You could try adding those manually using the rmrr Xen command line
> > >>>> option [0], maybe you can figure out which range(s) are missing?
> > >>>
> > >>> They seem to change, so it's hard to know. Would there be harm in
> > >>> adding one to cover the end of RAM ( 0x04,7c80,0000 ) to (
> > >>> 0xff,ffff,ffff )? Maybe that would just quiet the pointless faults
> > >>> while leaving the IOMMU enabled?
> > >>
> > >> While they may quieten the faults, I don't think those faults are
> > >> pointless. They indicate some problem with the software (less
> > >> likely the hardware, possibly the firmware) that you're using.
> > >> Also there's the question of what the overall behavior is going
> > >> to be when devices are permitted to access unpopulated address
> > >> ranges. I assume you did check already that no devices have their
> > >> BARs placed in that range?
> > >
> > > Isn't no-igfx already letting them try to read those unpopulated addresses?
> >
> > Yes, and it is for the reason that the documentation for the
> > option says "If specifying `no-igfx` fixes anything, please
> > report the problem." I imply from in in particular that one
> > better wouldn't use it for non-development purposes of whatever
> > kind.
>
> I stopped seeing these DMA faults, but I didn't know what made them go
> away. Then when working with an older 5.4.64 kernel, I saw them
> again. Eric bisected down to the 5.4.y version of mainline linux
> commit:
>
> commit 8195400f7ea95399f721ad21f4d663a62c65036f
> Author: Chris Wilson <chris@chris-wilson.co.uk>
> Date: Mon Oct 19 11:15:23 2020 +0100
>
> drm/i915: Force VT'd workarounds when running as a guest OS
>
> If i915.ko is being used as a passthrough device, it does not know if
> the host is using intel_iommu. Mixing the iommu and gfx causes a few
> issues (such as scanout overfetch) which we need to workaround inside
> the driver, so if we detect we are running under a hypervisor, also
> assume the device access is being virtualised.
So the commit above fixes the DMA faults seen on Linux when using a
i915 gfx card?
Thanks for digging into this.
Roger.
next prev parent reply other threads:[~2021-02-22 10:18 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-14 19:28 i915 dma faults on Xen Jason Andryuk
2020-10-14 19:37 ` Andrew Cooper
2020-10-15 11:31 ` Roger Pau Monné
2020-10-15 15:16 ` Jason Andryuk
2020-10-15 16:38 ` Tamas K Lengyel
2020-10-15 17:13 ` Jason Andryuk
2021-02-19 17:33 ` tboot UEFI and Xen (was Re: i915 dma faults on Xen) Jason Andryuk
2020-10-16 16:23 ` i915 dma faults on Xen Jason Andryuk
2020-10-21 9:58 ` Roger Pau Monné
2020-10-21 10:33 ` Jan Beulich
2020-10-21 10:51 ` Roger Pau Monné
2020-10-21 12:45 ` Jason Andryuk
2020-10-21 12:52 ` Jan Beulich
2020-10-21 13:36 ` Jason Andryuk
2020-10-21 13:59 ` Jan Beulich
2021-02-19 17:30 ` Jason Andryuk
2021-02-22 10:18 ` Roger Pau Monné [this message]
2021-02-22 12:49 ` Jason Andryuk
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YDOE35zhQYwgaxke@Air-de-Roger \
--to=roger.pau@citrix.com \
--cc=andrew.cooper3@citrix.com \
--cc=eric.chanudet@gmail.com \
--cc=intel-gfx@lists.freedesktop.org \
--cc=jandryuk@gmail.com \
--cc=jbeulich@suse.com \
--cc=xen-devel@lists.xenproject.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).