linux-kernel - [PATCH 0/2] x86/split_lock: Fix and cleanup of cpu_model_supports

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Message-ID: <20251218080044.2615106-1-xiaoyao.li@intel.com>
Date: Thu, 18 Dec 2025 16:00:42 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org
Cc: "H. Peter Anvin" <hpa@...or.com>,
	Tony Luck <tony.luck@...el.com>,
	linux-kernel@...r.kernel.org,
	xiaoyao.li@...el.com
Subject: [PATCH 0/2] x86/split_lock: Fix and cleanup of cpu_model_supports_sld

While considering Kiryl's suggestion[1], I'm wondering why we have
cpu_model_supports_sld defined, which seems like it could be replaced by
X86_FEATURE_SPLIT_LOCK_DETECT.

Tracing through the history, I find that X86_FEATURE_SPLIT_LOCK_DETECT
originally indicated whether the kernel enabled the split lock detection
feature, rather than enumerating hardware support for the feature, at the
time when cpu_model_supports_sld was introduced.

Now, the semantics of X86_FEATURE_SPLIT_LOCK_DETECT have changed and
it enuemrates the hardware support for the feature. Therefore, patch 2
replaces cpu_model_supports_sld with X86_FEATURE_SPLIT_LOCK_DETECT.

Patch 1 fixes a potential issue where MSR_TEST_CTRL can be written when
the split lock detection feature is not available, which can cause bizarre
behavior.

[1] https://lore.kernel.org/all/lvobu4gpfsjg63syubgy2jwcja72folflrst7bu2eqv6rhaqre@ttbkykphu32f/

Xiaoyao Li (2):
  x86/split_lock: Fix handling in split_lock_init()
  x86/split_lock: Drop cpu_model_supports_sld

 arch/x86/kernel/cpu/bus_lock.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

-- 
2.43.0