Re: [PATCH v3] arm64: add the printing of tpidr_elx in __show_regs()

Leizhen (ThunderTown)
2022-05-05T13:35:45Z

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@huawei.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.

>
>>
>> ... 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
>>>
>> .