linux-kernel - [PATCH 0/2] PCI: AtomicOps: Fix pci_enable_atomic_ops_to

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Message-Id: <20251110-fix_pciatops-v1-0-edc58a57b62e@linux.ibm.com>
Date: Mon, 10 Nov 2025 14:25:04 +0100
From: Gerd Bayer <gbayer@...ux.ibm.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>, Jay Cornwall <Jay.Cornwall@....com>,
        Felix Kuehling <Felix.Kuehling@....com>
Cc: Niklas Schnelle <schnelle@...ux.ibm.com>,
        Alexander Schmidt <alexs@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Gerd Bayer <gbayer@...ux.ibm.com>, Leon Romanovsky <leon@...nel.org>,
        stable@...r.kernel.org
Subject: [PATCH 0/2] PCI: AtomicOps: Fix pci_enable_atomic_ops_to_root()

Hi Bjorn et al.

this series addresses a few issues that have come up with the helper
function that enables Atomic Op Requests to be initiated by PCI
enpoints:

A. Most in-tree users of this helper use it incorrectly [0].
B. On s390, Atomic Op Requests are enabled, although the helper
   cannot know whether the root port is really supporting them.
C. Loop control in the helper function does not guarantee that a root
   port's capabilities are ever checked against those requested by the
   caller.

Address these issue with the following patches:
Patch 1: Make it harder to mis-use the enablement function,
Patch 2: Addresses issues B. and C.

I did test that issue B is fixed with these patches. Also, I verified
that Atomic Ops enablement on a Mellanox/Nvidia ConnectX-6 adapter
plugged straight into the root port of a x86 system still gets AtomicOp
Requests enabled. However, I did not test this with any PCIe switches
between root port and endpoint.

Ideally, both patches would be incorporated immediately, so we could
start correcting the mis-uses in the device drivers. I don't know of any
complaints when using Atomic Ops on devices where the driver is
mis-using the helper. Patch 2 however, is fixing an obseved issue.

[0]: https://lore.kernel.org/all/fbe34de16f5c0bf25a16f9819a57fdd81e5bb08c.camel@linux.ibm.com/
[1]: https://lore.kernel.org/all/20251105-mlxatomics-v1-0-10c71649e08d@linux.ibm.com/

Signed-off-by: Gerd Bayer <gbayer@...ux.ibm.com>
---
Gerd Bayer (2):
      PCI: AtomicOps: Define valid root port capabilities
      PCI: AtomicOps: Fix logic in enable function

 drivers/pci/pci.c             | 43 +++++++++++++++++++++----------------------
 include/uapi/linux/pci_regs.h |  8 ++++++++
 2 files changed, 29 insertions(+), 22 deletions(-)
---
base-commit: e9a6fb0bcdd7609be6969112f3fbfcce3b1d4a7c
change-id: 20251106-fix_pciatops-7e8608eccb03

Best regards,
-- 
Gerd Bayer <gbayer@...ux.ibm.com>