Re: [PATCH 01/21] arm64: entry: Defer setting of TPIDRRO_EL0 until exit to userspace

[Jinjie Ruan]

在 2026/9/8 0:42, Will Deacon 写道:
> In preparation for using TPIDRRO_EL0 to point at 'current' while running
> inside the kernel, defer its userspace initialisation from the
> context-switch patch to exception return. This has the added benefit of
> not having to worry about keeping the in-memory value and the register
> value in-sync during preemptible sections.
> 
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Signed-off-by: Will Deacon <will@xxxxxxxxxx>
> ---
>  arch/arm64/kernel/asm-offsets.c |  1 +
>  arch/arm64/kernel/entry.S       |  4 +++-
>  arch/arm64/kernel/process.c     | 16 +---------------
>  arch/arm64/kernel/sys_compat.c  |  7 -------
>  4 files changed, 5 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 9c853ed3ceab..6038ab3beb25 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -42,6 +42,7 @@ int main(void)
>  #endif
>    BLANK();
>    DEFINE(THREAD_CPU_CONTEXT,	offsetof(struct task_struct, thread.cpu_context));
> +  DEFINE(THREAD_TP_VALUE,	offsetof(struct task_struct, thread.uw.tp_value));
>    DEFINE(THREAD_SCTLR_USER,	offsetof(struct task_struct, thread.sctlr_user));
>  #ifdef CONFIG_ARM64_PTR_AUTH
>    DEFINE(THREAD_KEYS_USER,	offsetof(struct task_struct, thread.keys_user));
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index f63049ac32dc..59f045e496ec 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -47,7 +47,6 @@
>  	b	.Lskip_tramp_vectors_cleanup\@
>  	.if	\regsize == 64
>  	mrs	x30, tpidrro_el0
> -	msr	tpidrro_el0, xzr
>  	.else
>  	mov	x30, xzr
>  	.endif
> @@ -360,9 +359,12 @@ alternative_else_nop_endif
>  	.if	\el == 0
>  	ldr	x23, [sp, #S_SP]		// load return stack pointer
>  	msr	sp_el0, x23
> +	msr	tpidrro_el0, xzr
>  	tst	x22, #PSR_MODE32_BIT		// native task?
>  	b.eq	3f
>  
> +	ldr	x0, [tsk, #THREAD_TP_VALUE]
> +	msr	tpidrro_el0, x0

Reviewed-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>

>  #ifdef CONFIG_ARM64_ERRATUM_845719
>  alternative_if ARM64_WORKAROUND_845719
>  #ifdef CONFIG_PID_IN_CONTEXTIDR
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 581f80e9b9b7..bfdc12166895 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -256,17 +256,8 @@ static void tls_thread_flush(void)
>  	if (system_supports_tpidr2())
>  		write_sysreg_s(0, SYS_TPIDR2_EL0);
>  
> -	if (is_compat_task()) {
> +	if (is_compat_task())
>  		current->thread.uw.tp_value = 0;
> -
> -		/*
> -		 * We need to ensure ordering between the shadow state and the
> -		 * hardware state, so that we don't corrupt the hardware state
> -		 * with a stale shadow state during context switch.
> -		 */
> -		barrier();
> -		write_sysreg(0, tpidrro_el0);
> -	}
>  }
>  
>  static void flush_tagged_addr_state(void)
> @@ -531,11 +522,6 @@ static void tls_thread_switch(struct task_struct *next)
>  {
>  	tls_preserve_current_state();
>  
> -	if (is_compat_thread(task_thread_info(next)))
> -		write_sysreg(next->thread.uw.tp_value, tpidrro_el0);
> -	else
> -		write_sysreg(0, tpidrro_el0);
> -
>  	write_sysreg(*task_user_tls(next), tpidr_el0);
>  	if (system_supports_tpidr2())
>  		write_sysreg_s(next->thread.tpidr2_el0, SYS_TPIDR2_EL0);
> diff --git a/arch/arm64/kernel/sys_compat.c b/arch/arm64/kernel/sys_compat.c
> index 0451f96c2c3f..59eee301c6f4 100644
> --- a/arch/arm64/kernel/sys_compat.c
> +++ b/arch/arm64/kernel/sys_compat.c
> @@ -89,13 +89,6 @@ long compat_arm_syscall(struct pt_regs *regs, int scno)
>  
>  	case __ARM_NR_compat_set_tls:
>  		current->thread.uw.tp_value = regs->regs[0];
> -
> -		/*
> -		 * Protect against register corruption from context switch.
> -		 * See comment in tls_thread_flush.
> -		 */
> -		barrier();
> -		write_sysreg(regs->regs[0], tpidrro_el0);
>  		return 0;
>  
>  	default: