Re: [PATCH v2] arm64: add the printing of tpidr_elx in __show_regs()

Will Deacon
2022-04-28T10:24:04Z

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@huawei.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