arm64: mm: Allow forcing all userspace addresses to 52-bit

On arm64 52-bit VAs are provided to userspace when a hint is supplied to
mmap. This helps maintain compatibility with software that expects at
most 48-bit VAs to be returned.

In order to help identify software that has 48-bit VA assumptions, this
patch allows one to compile a kernel where 52-bit VAs are returned by
default on HW that supports it.

This feature is intended to be for development systems only.

Signed-off-by: Steve Capper <steve.capper@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 858e353b2f40..ca1f93233b22 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1186,6 +1186,19 @@ config ARM64_CNP
           at runtime, and does not affect PEs that do not implement
           this feature.
 
+config ARM64_FORCE_52BIT
+        bool "Force 52-bit virtual addresses for userspace"
+        depends on ARM64_52BIT_VA && EXPERT
+        help
+          For systems with 52-bit userspace VAs enabled, the kernel will attempt
+          to maintain compatibility with older software by providing 48-bit VAs
+          unless a hint is supplied to mmap.
+
+          This configuration option disables the 48-bit compatibility logic, and
+          forces all userspace addresses to be 52-bit on HW that supports it. One
+          should only enable this configuration option for stress testing userspace
+          memory management code. If unsure say N here.
+
 endmenu
 
 config ARM64_SVE