Re: Regression: "xhci: Fix command ring pointer corruption while aborting a command" breaks USB on Intel controllers

[Thorsten Leemhuis <regressions@leemhuis.info>]

Hi, this is your Linux kernel regression tracker speaking.

On 04.12.21 15:15, Hans de Goede wrote:
> 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.

FWIW, the commit is known to cause problems, one of them is found here:

https://lore.kernel.org/lkml/35f7428b39f996c793f5b4a6a314772681c73d7a.camel@apache.org/

This commit should improve the situation (and afaics hopefully fix all
problems related to it):

https://lore.kernel.org/stable/20211126122340.1193239-2-mathias.nyman@linux.intel.com/

Greg wants to sent it upstream today:

https://lore.kernel.org/lkml/YatGfEzzniH%2FSrn4@kroah.com/

Guess he soon after will backport it to the stable trees as well.

HTH, Ciao, Thorsten

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https://lore.kernel.org/lkml/35f7428b39f996c793f5b4a6a314772681c73d7a.camel@apache.org/