linux-usb.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Hans de Goede <hdegoede@redhat.com>
To: Mathias Nyman <mathias.nyman@intel.com>,
	Pavankumar Kondeti <pkondeti@codeaurora.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb <linux-usb@vger.kernel.org>
Subject: Regression: "xhci: Fix command ring pointer corruption while aborting a command" breaks USB on Intel controllers
Date: Sat, 4 Dec 2021 15:15:15 +0100	[thread overview]
Message-ID: <0a4d723c-221f-a42a-434c-34283a4cdab7@redhat.com> (raw)

Hi All,

There are several bug reports (arch and Fedora) about USB problems
starting with kernel 5.14.14 (5.14.13 is ok):

https://bugzilla.redhat.com/show_bug.cgi?id=2019788
https://bbs.archlinux.org/viewtopic.php?pid=2006862

And 5.16.6, which has the hub address0_mutex fixes does not
fix these problems for some users.

Looking at the history between those 2 commit ff0e50d3564f
("xhci: Fix command ring pointer corruption while aborting a command"):
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ff0e50d3564f

stood out to me as a possible cause of this. So I've build
a test 5.15.6 kernel for Fedora users with that commit reverted
and 2 users have now reported that this fixes things for them
(see https://bugzilla.redhat.com/show_bug.cgi?id=2019788).

The reason why this stood out to me is because doing a 32 bit
write over a possibly 64 bit databus to the xHCI controller may
result in the hw doing a 64 bit read + modify 32 bit + 64 bit write,
so I think that the following is happening after the commit:

sw: read 32 bit
hw: read 64 bit, return 32 bit
sw: modify it
sw: write 32 bit
hw: read 64 bit
hw: modify 32 bit of 64 bit wor5d
hw: write 64 bit

Which actually makes the chances of hitting the problem the commit
tries to fix larger on controllers using a 64 bit data bus.

Note this is just a theory, but it seems plausible to me.

All problem reports are people using integrated Intel xHCI controllers
which I believe are likely to use a 64 bit data-bus.

Regards,

Hans


             reply	other threads:[~2021-12-04 14:15 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-04 14:15 Hans de Goede [this message]
2021-12-05  6:46 ` Thorsten Leemhuis
2021-12-05  8:20   ` Greg Kroah-Hartman
2021-12-05  8:20 ` Greg Kroah-Hartman
2021-12-05 12:48   ` Greg Kroah-Hartman
2021-12-07  0:46     ` Tobias Bachmann

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=0a4d723c-221f-a42a-434c-34283a4cdab7@redhat.com \
    --to=hdegoede@redhat.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=linux-usb@vger.kernel.org \
    --cc=mathias.nyman@intel.com \
    --cc=pkondeti@codeaurora.org \
    --subject='Re: Regression: "xhci: Fix command ring pointer corruption while aborting a command" breaks USB on Intel controllers' \
    /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

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).