Subject: Re: [PATCH 3/4] ARM: remove support for highmem on VIVT

From: "Russell King (Oracle)" <[email-masked]>
Date: Fri, 2 Jan 2026 12:12:32 +0000

On Tue, Dec 23, 2025 at 10:26:12PM -0400, Jason Gunthorpe wrote:
> On Fri, Dec 19, 2025 at 09:34:33PM +0100, Arnd Bergmann wrote:
> > On Fri, Dec 19, 2025, at 18:14, Jason Gunthorpe wrote:
> > > On Fri, Dec 19, 2025 at 05:15:58PM +0100, Arnd Bergmann wrote:
> > >>  arch/arm/Kconfig                    |  1 +
> > >>  arch/arm/configs/gemini_defconfig   |  1 -
> > >>  arch/arm/configs/multi_v5_defconfig |  1 -
> > >>  arch/arm/configs/mvebu_v5_defconfig |  1 -
> > >>  arch/arm/include/asm/highmem.h      | 56 ++---------------------------
> > >>  arch/arm/mm/cache-feroceon-l2.c     | 31 ++--------------
> > >>  arch/arm/mm/cache-xsc3l2.c          | 47 +++---------------------
> > >>  arch/arm/mm/dma-mapping.c           | 12 ++-----
> > >>  arch/arm/mm/flush.c                 | 19 +++-------
> > >>  9 files changed, 16 insertions(+), 153 deletions(-)
> > >
> > > This looks great, but do you think there should be a boot time crash
> > > if a VIVT and HIGHMEM are enabled, just incase?
> > 
> > Do you mean in the common code or just for Arm?
> > 
> > We could use the Arm specific cache_is_vivt() macro, but it feels like
> > the 'dpends on !CPU_CACHE_VIVT' Kconfig check I added is both
> > safer and simpler.
> 
> Okay, so maybe I'm asking if !CPU_CACHE_VIVT then the kernel fails to
> boot on vivt systems, maybe it already does?

The cache modes (CPU_CACHE_xxx) are (were) selected by the processor
config entries. Not having the correct processor support built in to
the kernel will cause a boot failure.

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