linux-kernel - Re: [PATCH v2] arm64: add the printing of tpidr_elx in __show

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Date:   Thu, 28 Apr 2022 11:21:56 +0100
From:   Will Deacon <will@...nel.org>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        James Morse <james.morse@....com>
Subject: Re: [PATCH v2] arm64: add the printing of tpidr_elx in __show_regs()

On Wed, Mar 16, 2022 at 02:24:08PM +0800, Zhen Lei wrote:
> Commit 7158627686f0 ("arm64: percpu: implement optimised pcpu access
> using tpidr_el1") and commit 6d99b68933fb ("arm64: alternatives: use
> tpidr_el2 on VHE hosts") use tpidr_elx to cache my_cpu_offset to optimize
> pcpu access. However, when performing reverse execution based on the
> registers and the memory contents in kdump, this information is sometimes
> required if there is a pcpu access.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> ---
>  arch/arm64/kernel/process.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> v1 --> v2:
> Directly print the tpidr_elx register of the current exception level.
> Avoid coupling with the implementation of 'my_cpu_offset'.
> 
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 5369e649fa79ff8..738932e6fa4e947 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -216,6 +216,17 @@ void __show_regs(struct pt_regs *regs)
>  	show_regs_print_info(KERN_DEFAULT);
>  	print_pstate(regs);
>  
> +	switch (read_sysreg(CurrentEL)) {

This should use is_kernel_in_hyp_mode() to detect if we're running at El2.

> +	case CurrentEL_EL1:
> +		printk("tpidr_el1 : %016llx\n", read_sysreg(TPIDR_EL1));
> +		break;
> +	case CurrentEL_EL2:
> +		printk("tpidr_el2 : %016llx\n", read_sysreg(TPIDR_EL2));
> +		break;
> +	default:
> +		break;
> +	}

I think this path can be triggered directly from usermode, so we really
shouldn't be printing raw kernel virtual addresses here.

Will