linux-kernel - [PATCH v2 0/2] x86/cpu/intel: Add RFDS mitigation quirk for Goldmont and Tremont-D

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Message-ID: <20260130123340.1544-1-moontorise@cfg.kr>
Date: Fri, 30 Jan 2026 21:33:38 +0900
From: Joongsun Moon-Lee <moontorise@....kr>
To: x86@...nel.org,
	Thomas Gleixner <tglx@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H . Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	linux-kernel@...r.kernel.org,
	Joongsun Moon-Lee <moontorise@....kr>
Subject: [PATCH v2 0/2] x86/cpu/intel: Add RFDS mitigation quirk for Goldmont and Tremont-D

Greetings,

I would like to thank Dave Hansen for the insightful feedback on the
first version; the suggested refactoring has significantly improved
the clarity and structure of this series.

This is the second version of the patch series to support RFDS mitigation
specifically for Goldmont and Tremont-D processors.

While most affected processors received microcode updates [1] to enumerate
the RFDS_CLEAR bit, Goldmont and Tremont-D support the VERW-based
mitigation but fail to report it via MSR. This series provides
an implicit quirk to enable protection for these models.

Changes since v1:
- Split the original patch into two parts as suggested by Dave Hansen:
  1. x86/cpu: Refactor RFDS mitigation to use X86_FEATURE_RFDS_CLEAR
  2. x86/cpu/intel: Add implicit RFDS mitigation for Goldmont and Tremont-D
- Improved the quirk detection logic: Instead of manual revision checks,
  it now leverages X86_BUG_OLD_MICROCODE.

Technical Note on Tremont-D:
According to Intel's guidance [2], Tremont-D stepping 7 is listed as
"MCU + Software" mitigatable. However, as no microcode update has been
observed for this model, patch 2 identifies Tremont-D stepping 7 implicitly
to enable VERW mitigation. This approach aligns with Intel's documented
strategy, even though the actual VERW side-effects on this microcode
cannot be independently verified.

[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/releases/tag/microcode-20240312
[2] https://www.intel.com/content/www/us/en/developer/topic-technology/software-security-guidance/processors-affected-consolidated-product-cpu-model.html#tab-blade-1-1

Link: https://lore.kernel.org/all/20260129154342.3867-1-moontorise@cfg.kr/
Signed-off-by: Joongsun Moon-Lee <moontorise@....kr>

Joongsun Moon-Lee (2):
  x86/cpu: Refactor RFDS mitigation to use X86_FEATURE_RFDS_CLEAR
  x86/cpu/intel: Add implicit RFDS mitigation for Goldmont and Tremont-D

 arch/x86/include/asm/cpufeatures.h |  1 +
 arch/x86/kernel/cpu/bugs.c         | 12 +++++-------
 arch/x86/kernel/cpu/intel.c        | 14 ++++++++++++++
 3 files changed, 20 insertions(+), 7 deletions(-)

-- 
2.52.0