linux-hardening - Re: [Intel-wired-lan] [PATCH v2] igc: Ignore AER reset when device is suspended

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Message-ID: <20230715191216.GA364070@bhelgaas>
Date:   Sat, 15 Jul 2023 14:12:16 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Vinicius Costa Gomes <vinicius.gomes@...el.com>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Tony Luck <tony.luck@...el.com>,
        Kees Cook <keescook@...omium.org>, linux-pci@...r.kernel.org,
        jesse.brandeburg@...el.com, linux-kernel@...r.kernel.org,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
        Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
        anthony.l.nguyen@...el.com, linux-hardening@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [Intel-wired-lan] [PATCH v2] igc: Ignore AER reset when device
 is suspended

On Fri, Jul 14, 2023 at 01:35:55PM -0700, Vinicius Costa Gomes wrote:
> Bjorn Helgaas <helgaas@...nel.org> writes:
> > On Fri, Jul 14, 2023 at 01:05:41PM +0800, Kai-Heng Feng wrote:
> >> When a system that connects to a Thunderbolt dock equipped with I225,
> >> like HP Thunderbolt Dock G4, I225 stops working after S3 resume:
> >> ...
> >
> >> The issue is that the PTM requests are sending before driver resumes the
> >> device. Since the issue can also be observed on Windows, it's quite
> >> likely a firmware/hardware limitation.
> >
> > Does this mean we didn't disable PTM correctly on suspend?  Or is the
> > device defective and sending PTM requests even though PTM is disabled?
> 
> The way I understand the hardware bug, the device is defective, as you
> said, the device sends PTM messages when "busmastering" is disabled.

Bus Master Enable controls the ability of a Function to issue Memory
and I/O Read/Write Requests (PCIe r6.0, sec 7.5.1.1.3).  PTM uses
Messages, and I don't think they should be affected by Bus Master
Enable.

I also don't understand the I225 connection.  We have these
Uncorrected Non-Fatal errors:

> >> [  606.527931] pcieport 0000:00:1d.0: AER: Multiple Uncorrected (Non-Fatal) error received: 0000:00:1d.0
> >> [  606.528064] pcieport 0000:00:1d.0: PCIe Bus Error: severity=Uncorrected (Non-Fatal), type=Transaction Layer, (Requester ID)
> >> [  606.528068] pcieport 0000:00:1d.0:   device [8086:7ab0] error status/mask=00100000/00004000
> >> [  606.528072] pcieport 0000:00:1d.0:    [20] UnsupReq               (First)
> >> [  606.528075] pcieport 0000:00:1d.0: AER:   TLP Header: 34000000 0a000052 00000000 00000000
> >> [  606.528079] pcieport 0000:00:1d.0: AER:   Error of this Agent is reported first
> >> [  606.528098] pcieport 0000:04:01.0: PCIe Bus Error: severity=Uncorrected (Non-Fatal), type=Transaction Layer, (Requester ID)
> >> [  606.528101] pcieport 0000:04:01.0:   device [8086:1136] error status/mask=00300000/00000000
> >> [  606.528105] pcieport 0000:04:01.0:    [20] UnsupReq               (First)
> >> [  606.528107] pcieport 0000:04:01.0:    [21] ACSViol
> >> [  606.528110] pcieport 0000:04:01.0: AER:   TLP Header: 34000000 04000052 00000000 00000000

They are clearly Unsupported Request errors caused by PTM Requests
(decoding at https://bugzilla.kernel.org/show_bug.cgi?id=216850#c9),
but they were logged by 00:1d.0 and 04:01.0.

The hierarchy is this:

  00:1d.0 Root Port to [bus 03-6c]
  03:00.0 Switch Upstream Port to [bus 04-6c]
  04:01.0 Switch Downstream Port to [bus 06-38]
  06:00.0 Switch Upstream Port to [bus 07-38]
  07:04.0 Switch Downstream Port to [bus 38]
  38:00.0 igc I225 NIC

If I225 sent a PTM request when it shouldn't have, i.e., when 07:04.0
didn't have PTM enabled, the error would have been logged by 07:04.0.

The fact that the errors were logged by 00:1d.0 and 04:01.0 means that
they were caused by PTM requests from 03:00.0 and 06:00.0.

Bjorn