linux-kernel - Re: [PATCH v2 0/4] x86/mtrr: Allow MTRR updates on multiple CPUs in parallel

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Message-ID: <35527cf2-322f-410b-9942-5cba0956b237@suse.com>
Date: Mon, 9 Feb 2026 10:12:59 +0100
From: Juergen Gross <jgross@...e.com>
To: linux-kernel@...r.kernel.org, x86@...nel.org
Cc: 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: Re: [PATCH v2 0/4] x86/mtrr: Allow MTRR updates on multiple CPUs in
 parallel

Ping?

I'd really like to have this in 7.0, as it is fixing a real issue on
some machines ...


Juergen

On 30.01.26 12:36, Juergen Gross wrote:
> 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.
> 
> Changes in V2:
> - fix a function comment header in patch 2
> 
> 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 | 139 ++++++++++++++++++++++++-----
>   arch/x86/kernel/cpu/mtrr/mtrr.c    |   3 +
>   arch/x86/kernel/cpu/mtrr/mtrr.h    |   2 +
>   6 files changed, 122 insertions(+), 106 deletions(-)
> 


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