linux-kernel - [PATCH 0/4] x86/mtrr: Allow MTRR updates on multiple CPUs in parallel

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Message-ID: <20260121141106.755458-1-jgross@suse.com>
Date: Wed, 21 Jan 2026 15:11:02 +0100
From: Juergen Gross <jgross@...e.com>
To: linux-kernel@...r.kernel.org,
	x86@...nel.org
Cc: Juergen Gross <jgross@...e.com>,
	Thomas Gleixner <tglx@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 0/4] x86/mtrr: Allow MTRR updates on multiple CPUs in parallel

Today MTRR updates are serialized to not happen on multiple CPUs at the
same time, as the related coding is using global variables.

On huge machines with lots of CPUs this can result in problems, as such
updates are happening through stop_machine(), which will call the MTRR
update function with interrupts off on all CPUs at the same time. The
interrupts will be switched on only after the last CPU has finished
the MTRR update. As the update is required to run in uncached mode, it
can take easily several milliseconds on each CPU, resulting in the
whole process to need several seconds. This in turn can cause the
watchdog to trigger and to recognize a hard system lockup.

This series is changing the behavior by allowing the MTRR update to
happen on all CPUs in parallel.

Juergen Gross (4):
  x86/mtrr: Move cache_enable() and cache_disable() to mtrr/generic.c
  x86/mtrr: Introduce MTRR work state structure
  x86/mtrr: Add a prepare_set hook to mtrr_ops
  x86/mtrr: Drop cache_disable_lock

 arch/x86/include/asm/cacheinfo.h   |   2 -
 arch/x86/include/asm/mtrr.h        |   2 -
 arch/x86/kernel/cpu/cacheinfo.c    |  80 +----------------
 arch/x86/kernel/cpu/mtrr/generic.c | 137 ++++++++++++++++++++++++-----
 arch/x86/kernel/cpu/mtrr/mtrr.c    |   3 +
 arch/x86/kernel/cpu/mtrr/mtrr.h    |   2 +
 6 files changed, 120 insertions(+), 106 deletions(-)

-- 
2.52.0