> On Fri, Sep 19, 2025, at 16:34, Jason Gunthorpe wrote: > > On Fri, Sep 19, 2025 at 04:22:20PM +0200, Arnd Bergmann wrote: [...] > > I am right it sounds like we can drop vivt cache support with highmem? > > vivt is alot easier to understand if kmap isn't running around > > creating virtual addresses aliases! > > I think so, yes. I've prototyped a patch for it to add a dependency > on !VIVT and the drop the code paths that are clearly no longer > needed without it. This obviously needs proper testing, but the > diffstat is promising: > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index f14bac913d50..0a31cfaf3818 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -1214,6 +1214,7 @@ config ARCH_SPARSEMEM_ENABLE > config HIGHMEM > bool "High Memory Support" > depends on MMU > + depends on !CPU_CACHE_VIVT > select KMAP_LOCAL > select KMAP_LOCAL_NON_LINEAR_PTE_ARRAY > help > 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 | 14 ++---- > arch/arm/mm/flush.c | 19 ++------ > mm/highmem.c | 86 > +++++-------------------------------- > 10 files changed, 27 insertions(+), 230 deletions(-) > > I did get an email from Nicolas Schichan (added to Cc here), > and he is still supporting a widely deployed Kirkwood based > platform that uses 1GB RAM configurations. He should get > a chance to test that with CONFIG_VMSPLIT_3G_OPT, but I > would expect that to continue working, possibly with minor > bugfixes.
Hello Arnd, We don't use HIGMEM on our Kirkwood platform, we are happy using a 2G/2G WMSPLIT. We don't need a lot of virtual address space for userland, and with the 2G split we don't waste physical memory. I'm happy to test your patch serie with VMSPLIT_3G_OPT and see if it still boots with it once you send it. Regards, -- Nicolas Schichan
