linux-kernel - Re: [PATCH v6 5/5] arm64: futex: support futex with FEAT

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Message-ID: <aJ9oIes7LLF3Nsp1@arm.com>
Date: Fri, 15 Aug 2025 18:02:25 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: will@...nel.org, broonie@...nel.org, maz@...nel.org,
	oliver.upton@...ux.dev, shameerali.kolothum.thodi@...wei.com,
	joey.gouly@....com, james.morse@....com, ardb@...nel.org,
	scott@...amperecomputing.com, suzuki.poulose@....com,
	yuzenghui@...wei.com, mark.rutland@....com,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 5/5] arm64: futex: support futex with FEAT_LSUI

On Mon, Aug 11, 2025 at 05:36:35PM +0100, Yeoreum Yun wrote:
> +#ifdef CONFIG_AS_HAS_LSUI
> +
> +#define __LSUI_PREAMBLE	".arch_extension lsui\n"
> +
> +#define LSUI_FUTEX_ATOMIC_OP(op, asm_op, mb)				\
> +static __always_inline int						\
> +__lsui_futex_atomic_##op(int oparg, u32 __user *uaddr, int *oval)	\
> +{									\
> +	int ret = 0;							\
> +	int val;							\
> +									\
> +	mte_enable_tco();						\

The reason uaccess_disable_privileged() sets the MTE TCO (tag check
override) is because the user and the kernel may have different settings
for tag checking. If we use the user instructions provided by FEAT_LSUI,
we leave the MTE checking as is.

The same comment for all the other functions here.

-- 
Catalin