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Date: Sat, 27 Apr 2024 10:41:45 +0300
From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Lukas Wunner <lukas@wunner.de>
Cc: Esther Shimanovich <eshimanovich@chromium.org>,
	Mario Limonciello <mario.limonciello@amd.com>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Bjorn Helgaas <bhelgaas@google.com>, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org, Rajat Jain <rajatja@google.com>,
	Gil Fine <gil.fine@linux.intel.com>
Subject: Re: [PATCH v4] PCI: Relabel JHL6540 on Lenovo X1 Carbon 7,8
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On Sat, Apr 27, 2024 at 07:35:33AM +0200, Lukas Wunner wrote:
> On Fri, Apr 26, 2024 at 07:52:07AM +0300, Mika Westerberg wrote:
> > On Thu, Apr 25, 2024 at 05:16:24PM -0400, Esther Shimanovich wrote:
> > > I did find one example of a docking station that uses the DSL6540
> > > chip, which has PCI IDs defined in include/linux/pci_ids.h:
> > > #define PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_4C_NHI     0x1577
> > > #define PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_4C_BRIDGE  0x1578
> > > It seems like it has an NHI, despite being in an external, removable
> > > docking station. This appears to contradict what you say about only
> > > having "NHI" on a host router. I am assuming that by host router, you
> > > mean the fixed discrete, fixed thunderbolt chip, or the thunderbolt
> > > controller upstream to the root port. Please correct me if I got
> > > anything wrong!
> > 
> > So it goes same way with other discrete chips from Intel at least. It is
> > the same silicon but the NHI is disabled on device routers.
> > 
> > That said, it is entirely possible for a "malicious" device to pretend
> > to have one so we need to be careful.
> 
> If a device (accidentally or maliciously) exposes an NHI, the thunderbolt
> driver will try to bind to it.
> 
> Do we take any precautions to prevent that?

Not at the moment but it will be behind the IOMMU so it cannot access
any other memory that what is reserved for it.

> AFAICS we'd be allocating a duplicate root_switch with route 0.
> Seems dangerous if two driver instances talk to the same Root Switch.

I don't think it even works because it cannot have topology ID of 0 if
it is a device router which it is in this case since it is being first
enumerated by the "real" host.

That said we have not tested this either so can be 100% sure.