Re: [PATCH] arm64: Optionally disable EL0 MTE via command-line

[Catalin Marinas]

On Fri, Feb 13, 2026 at 12:51:07PM +0100, Pierre-Clément Tosi wrote:
> Although it is currently possible to fully disable MTE on MTE-capable
> CPUs (with arm64.nomte or id_aa64pfr1.mte=0) and to only use MTE in
> userspace (with kasan=off), there is no way to limit the use of MTE to
> the kernel because CPU capabilities are traditionally exposed directly
> to userspace.
> 
> To address this, introduce a new cmdline argument (inspired by the
> existing arm64.nomte) to only expose the MTE capability of the CPU to
> the kernel. Combined with KASAN, this results in only the kernel using
> the feature, while HWCAP2_MTE and the corresponding MSR ID_AA64PFR1_EL1
> field are hidden from userspace.
[...]
> +	arm64.nomte_el0	[ARM64] Unconditionally disable Memory Tagging Extension
> +			support for userspace

Why would we need this? It's a user-space choice whether it uses MTE or
not. It's not like the kernel is forcing it onto the user processes.

-- 
Catalin