From: Arnd Bergmann <arnd@kernel•org>
To: linux-mm@kvack•org
Cc: Arnd Bergmann <arnd@arndb•de>,
Andrew Morton <akpm@linux-foundation•org>,
Andreas Larsson <andreas@gaisler•com>,
Christophe Leroy <chleroy@kernel•org>,
Dave Hansen <dave.hansen@linux•intel.com>,
Jason Gunthorpe <jgg@nvidia•com>,
Linus Walleij <linus.walleij@linaro•org>,
Matthew Wilcox <willy@infradead•org>,
Richard Weinberger <richard@nod•at>,
Russell King <linux@armlinux•org.uk>,
linux-arm-kernel@lists•infradead.org,
linux-fsdevel@vger•kernel.org, linuxppc-dev@lists•ozlabs.org,
x86@kernel•org
Subject: [PATCH 2/4] ARM: add CONFIG_VMSPLIT_2G_OPT option
Date: Fri, 19 Dec 2025 17:15:57 +0100 [thread overview]
Message-ID: <20251219161559.556737-3-arnd@kernel.org> (raw)
In-Reply-To: <20251219161559.556737-1-arnd@kernel.org>
From: Arnd Bergmann <arnd@arndb•de>
Unlike x86 and powerpc, there is currently no option to use exactly 2GiB
of lowmem on Arm. Since 2GiB is still a relatively common configuration
on embedded systems, it makes sense to allow this to be used in
non-highmem builds.
Add the Kconfig option and make this the default for non-LPAE builds
with highmem enabled instead of CONFIG_VMSPLIT_2G. LPAE still requires
the vmsplit to be on a gigabyte boundary, so this is only available for
classic pagetables at the moment, same as CONFIG_VMSPLIT_3G_OPT.
Tested in qemu -M virt, both with and without HIGHMEM enabled.
Signed-off-by: Arnd Bergmann <arnd@arndb•de>
---
arch/arm/Kconfig | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 7c0ac017e086..921ea61aa96e 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1009,7 +1009,8 @@ config BL_SWITCHER_DUMMY_IF
choice
prompt "Memory split"
depends on MMU
- default VMSPLIT_2G if HIGHMEM || ARM_LPAE
+ default VMSPLIT_2G if ARM_LPAE
+ default VMSPLIT_2G_OPT if HIGHMEM
default VMSPLIT_3G_OPT
help
Select the desired split between kernel and user memory.
@@ -1026,6 +1027,9 @@ choice
bool "3G/1G user/kernel split (for full 1G low memory)"
config VMSPLIT_2G
bool "2G/2G user/kernel split"
+ config VMSPLIT_2G_OPT
+ depends on !ARM_LPAE
+ bool "2G/2G user/kernel split (for full 2G low memory)"
config VMSPLIT_1G
bool "1G/3G user/kernel split"
endchoice
@@ -1034,6 +1038,7 @@ config PAGE_OFFSET
hex
default PHYS_OFFSET if !MMU
default 0x40000000 if VMSPLIT_1G
+ default 0x70000000 if VMSPLIT_2G_OPT
default 0x80000000 if VMSPLIT_2G
default 0xB0000000 if VMSPLIT_3G_OPT
default 0xC0000000
@@ -1042,6 +1047,7 @@ config KASAN_SHADOW_OFFSET
hex
depends on KASAN
default 0x1f000000 if PAGE_OFFSET=0x40000000
+ default 0x4f000000 if PAGE_OFFSET=0x70000000
default 0x5f000000 if PAGE_OFFSET=0x80000000
default 0x9f000000 if PAGE_OFFSET=0xC0000000
default 0x8f000000 if PAGE_OFFSET=0xB0000000
--
2.39.5
next prev parent reply other threads:[~2025-12-19 16:17 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-19 16:15 [PATCH 0/4] mm: increase lowmem size in linux-7.0 Arnd Bergmann
2025-12-19 16:15 ` [PATCH 1/4] arch/*: increase lowmem size to avoid highmem use Arnd Bergmann
2025-12-19 18:02 ` Dave Hansen
2025-12-19 20:20 ` Arnd Bergmann
2025-12-19 20:52 ` Dave Hansen
2025-12-20 12:17 ` Arnd Bergmann
2026-01-06 17:01 ` Dave Hansen
2025-12-21 9:30 ` David Hildenbrand (Red Hat)
2025-12-21 15:26 ` H. Peter Anvin
2025-12-24 11:35 ` Christophe Leroy (CS GROUP)
2026-01-08 14:32 ` Christophe Leroy (CS GROUP)
2025-12-19 16:15 ` Arnd Bergmann [this message]
2025-12-19 16:15 ` [PATCH 3/4] ARM: remove support for highmem on VIVT Arnd Bergmann
2025-12-19 17:14 ` Jason Gunthorpe
2025-12-19 20:34 ` Arnd Bergmann
2025-12-24 2:26 ` Jason Gunthorpe
2025-12-24 10:39 ` Arnd Bergmann
2026-01-02 12:12 ` Russell King (Oracle)
2025-12-19 16:15 ` [PATCH 4/4] mm: remove ARCH_NEEDS_KMAP_HIGH_GET Arnd Bergmann
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