linux-kernel - Re: [RFC PATCH 0/2] vfio/pci: Block and audit accesses to unassigned config regions

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Message-Id: <20250517171459.15231-1-chath@bu.edu>
Date: Sat, 17 May 2025 17:14:59 +0000
From: Chathura Rajapaksha <chathura.abeyrathne.lk@...il.com>
To: jgg@...pe.ca
Cc: Yunxiang.Li@....com,
	alex.williamson@...hat.com,
	audit@...r.kernel.org,
	avihaih@...dia.com,
	bhelgaas@...gle.com,
	chath@...edu,
	chathura.abeyrathne.lk@...il.com,
	eparis@...hat.com,
	giovanni.cabiddu@...el.com,
	kevin.tian@...el.com,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	paul@...l-moore.com,
	schnelle@...ux.ibm.com,
	xin.zeng@...el.com,
	yahui.cao@...el.com,
	zhangdongdong@...incomputing.com
Subject: Re: [RFC PATCH 0/2] vfio/pci: Block and audit accesses to unassigned config regions

On Fri, May 16, 2025 at 2:35 PM Jason Gunthorpe <jgg@...pe.ca> wrote:
> > By PCI bus error, I was referring to AER-reported uncorrectable errors.
> > For example:
> > pcieport 0000:c0:01.1: PCIe Bus Error: severity=Uncorrected (Fatal), type=Transaction Layer, (Requester ID)
> > pcieport 0000:c0:01.1:   device [1022:1483] error status/mask=00004000/07a10000
> > pcieport 0000:c0:01.1:    [14] CmpltTO                (First)
>
> That's sure looks like a device bug. You should not ever get time out
> for a config space read.

Just to clarify, the above error was triggered by a write to the
configuration space. In fact, all the errors we have observed so far
were triggered by writes to unassigned PCI config space regions.

> Dynamically updateable might be overkill, I think you have one
> defective device. Have you talked to the supplier to see if it can be
> corrected?

So far, we have seen this issue on five PCIe devices across GPU and
storage classes from two different vendors. Therefore, we suspect the
problem is not limited to a single device, vendor, or class of devices.
We reported the issue to both vendors over two months ago. But we
have not gained any insights into the root cause of the issue from
either vendor so far.

> Alternatively you could handle this in qemu by sanitizing the config
> space..

While it's possible to address this issue for QEMU-KVM guests by
modifying QEMU, PCIe devices can also be assigned directly to
user-space applications such as DPDK via VFIO. We thought addressing
this at the VFIO driver level would help mitigate the issue in a
broader context beyond virtualized environments.

Thanks,
Chathura