linux-kernel - Re: [PATCH v3] arm64: add the printing of tpidr_elx in __show

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Message-ID: <7c1207fa-56aa-1b33-31fd-3ec395b08f2b@huawei.com>
Date:   Fri, 6 May 2022 16:16:55 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Mark Rutland <mark.rutland@....com>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] arm64: add the printing of tpidr_elx in __show_regs()



On 2022/5/5 21:34, Leizhen (ThunderTown) wrote:
> 
> 
> On 2022/5/5 21:26, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2022/5/5 21:04, Mark Rutland wrote:
>>> On Thu, May 05, 2022 at 05:56:40PM +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 | 5 +++++
>>>>  1 file changed, 5 insertions(+)
>>>>
>>>> v2 --> v3:
>>>> 1) Relace "switch (read_sysreg(CurrentEL))" statement with
>>>>    "if (is_kernel_in_hyp_mode())" statement.
>>>> 2) Change the register name to lowercase.
>>>>
>>>> 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 7fa97df55e3ad3f..7b6bccce9721c36 100644
>>>> --- a/arch/arm64/kernel/process.c
>>>> +++ b/arch/arm64/kernel/process.c
>>>> @@ -216,6 +216,11 @@ void __show_regs(struct pt_regs *regs)
>>>>  	show_regs_print_info(KERN_DEFAULT);
>>>>  	print_pstate(regs);
>>>>  
>>>> +	if (is_kernel_in_hyp_mode())
>>>> +		printk("tpidr_el2 : %016llx\n", read_sysreg(tpidr_el2));
>>>> +	else
>>>> +		printk("tpidr_el1 : %016llx\n", read_sysreg(tpidr_el1));
>>>
>>> If we care about the offset specifically, this would be simpler as:
>>>
>>> 	printk("cpu offset : 0x%016lx\n", __my_cpu_offset());
>>
>> The function name is __show_regs(), so not using register name may not be good.
>> In fact, some other architectures may also have this problem. If we use my_cpu_offset,
>> we may need to put it in a public.
> 
> The other idea is to back up each my_cpu_offset in an array. In this way, the offset can
> be queried through vmcore even if it is not printed.

Sorry, __per_cpu_offset[NR_CPUS] is always defined.

> 
>>
>>>
>>> ... which should do the right thing even if we repurpose the TPIDRs and move the offset elsewhere.
>>>
>>> As Will says, we should only log this for !user_mode(regs), so it could
>>> be placed in the block below, immediately before we print the kernel PC, i.e.
>>>
>>> 	if (!user_mode_regs) {
>>> 		printk("cpu offset : %016lx\n", __my_cpu_offset());
>>> 		printk("pc : %pS\n", (void *)regs->pc);
>>> 		printk("lr : %pS\n", (void *)ptrauth_strip_insn_pac(lr));
>>> 		...
>>> 	}
>>>
>>> ... or in a separate block which checks the same condition.
>>>
>>> Thanks,
>>> Mark.
>>>
>>>> +
>>>>  	if (!user_mode(regs)) {
>>>>  		printk("pc : %pS\n", (void *)regs->pc);
>>>>  		printk("lr : %pS\n", (void *)ptrauth_strip_insn_pac(lr));
>>>> -- 
>>>> 2.25.1
>>>>
>>> .
>>>
>>
> 

-- 
Regards,
  Zhen Lei