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

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Date:   Thu, 28 Apr 2022 19:07:51 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Will Deacon <will@...nel.org>
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 2022/4/28 18:21, Will Deacon wrote:
> 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.

I run echo c > /proc/sysrq-trigger and didn't trigger this path, but maybe
there's another way. Analysis from the other side, except for the instruction
address, all generic registers r0-r31 is output as raw. There's also an
opportunity to contain the instruction address.

So how about:
+       if (oops_in_progress)
+               printk("tpidr : %016lx\n", __my_cpu_offset);

> 
> Will
> .
> 

-- 
Regards,
  Zhen Lei