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

Leizhen (ThunderTown)
2022-04-28T11:13:28Z

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@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.

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