---
id: CVE-2026-64590
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning

  When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf into a DRM
  driver (e.g
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning

  When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf into a DRM
  driver (e.g. amdgpu fo…
severity: none
published: '2026-08-06'
updated: '2026-08-23'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-64590'
references:
  - url: 'https://git.kernel.org/stable/c/01126abc11bcc6a45b664293b0b5df715be911d7'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/0449a6583c0ee76778d314e4e82f166fc97fa9d8'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/0db56e7eae932f8e2f3eb44ad1a63633d8f504f8'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/34696563461c9a23177feb6d8aff43f4c0510278'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/4a7c644e632741c2a3116a0d3da6c11de957a6ba'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/504e2b4ab97a51d56d966cd36d0997ad30b65b2d'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d6552f5cff795d60e629f37513ecf23d88fd2f82'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/dd7f1e572f44d3d039dc77e3989f537196c3bf52'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.0022
epssPercentile: 0.11014
ingestedAt: '2026-08-23T13:48:05.710Z'
---

## Overview

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

dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning

When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf into a DRM
driver (e.g. amdgpu for video playback in GNOME Videos / Showtime)
triggers a spurious warning:

  DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \
      overlapping mappings aren't supported
  WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0

The call chain is:

  amdgpu_cs_ioctl
   -> amdgpu_ttm_backend_bind
    -> dma_buf_map_attachment
     -> [udmabuf] map_udmabuf -> get_sg_table
      -> dma_map_sgtable(dev, sg, direction, 0)  // attrs=0
       -> debug_dma_map_sg -> add_dma_entry -> EEXIST

This happens because udmabuf builds a per-page scatter-gather list via
sg_set_folio().  When begin_cpu_udmabuf() has already created an sg
table mapped for the misc device, and an importer such as amdgpu maps
the same pages for its own device via map_udmabuf(), the DMA debug
infrastructure sees two active mappings whose physical addresses share
cacheline boundaries and warns about the overlap.

The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in
add_dma_entry() because it signals that no CPU cache maintenance is
performed at map/unmap time, making the cacheline overlap harmless.

All other major dma-buf exporters already pass this flag:
  - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC
  - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC

The CPU sync at map/unmap time is also redundant for udmabuf:
begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit
cache synchronization via dma_sync_sgtable_for_cpu/device() when CPU
access is requested through the dma-buf interface.

Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and
dma_unmap_sgtable() in udmabuf to suppress the spurious warning and
skip the redundant sync.

## Remediation

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