---
id: CVE-2025-39784
title: 'PCI: Fix link speed calculation on retrain failure'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  PCI: Fix link speed calculation on retrain failure

  When pcie_failed_link_retrain() fails to retrain, it tries to revert to the
  previous link speed.  However it calcula…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= de9a6c8d5dbfedb5eb3722c822da0490f6a59a45 <
    16557320f378262b5c605b15edebd3642406992a
  - >-
    Linux >= de9a6c8d5dbfedb5eb3722c822da0490f6a59a45 <
    9989e0ca7462c62f93dbc62f684448aa2efb9226
  - Linux 6.13
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-05T21:11:28.690357Z'
published: '2025-09-11'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T21:12:58.115Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-39784'
references:
  - url: 'https://git.kernel.org/stable/c/16557320f378262b5c605b15edebd3642406992a'
  - url: 'https://git.kernel.org/stable/c/9989e0ca7462c62f93dbc62f684448aa2efb9226'
tags:
  - cve.org
epss: 0.0013
epssPercentile: 0.02675
ingestedAt: '2026-11-05T22:38:32.027Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

PCI: Fix link speed calculation on retrain failure

When pcie_failed_link_retrain() fails to retrain, it tries to revert to the
previous link speed.  However it calculates that speed from the Link
Control 2 register without masking out non-speed bits first.

PCIE_LNKCTL2_TLS2SPEED() converts such incorrect values to
PCI_SPEED_UNKNOWN (0xff), which in turn causes a WARN splat in
pcie_set_target_speed():

  pci 0000:00:01.1: [1022:14ed] type 01 class 0x060400 PCIe Root Port
  pci 0000:00:01.1: broken device, retraining non-functional downstream link at 2.5GT/s
  pci 0000:00:01.1: retraining failed
  WARNING: CPU: 1 PID: 1 at drivers/pci/pcie/bwctrl.c:168 pcie_set_target_speed
  RDX: 0000000000000001 RSI: 00000000000000ff RDI: ffff9acd82efa000
  pcie_failed_link_retrain
  pci_device_add
  pci_scan_single_device

Mask out the non-speed bits in PCIE_LNKCTL2_TLS2SPEED() and
PCIE_LNKCAP_SLS2SPEED() so they don't incorrectly return PCI_SPEED_UNKNOWN.

[bhelgaas: commit log, add details from https://lore.kernel.org/r/1c92ef6bcb314ee6977839b46b393282e4f52e74.1750684771.git.lukas@wunner.de]

## Affected

- `Linux >= de9a6c8d5dbfedb5eb3722c822da0490f6a59a45 < 16557320f378262b5c605b15edebd3642406992a`
- `Linux >= de9a6c8d5dbfedb5eb3722c822da0490f6a59a45 < 9989e0ca7462c62f93dbc62f684448aa2efb9226`
- `Linux 6.13`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.