Re: [RESEND PATCH v5 5/5] Documentation/vmcoreinfo: Add documentation for 'TCR_EL1.T1SZ'

Bhupesh Sharma
2019-12-25T18:49:58Z

Hi James,

On 12/12/2019 04:02 PM, James Morse wrote:
> Hi Bhupesh,

I am sorry this review mail skipped my attention due to holidays and
focus on other urgent issues.

> On 29/11/2019 19:59, Bhupesh Sharma wrote:
>> Add documentation for TCR_EL1.T1SZ variable being added to
>> vmcoreinfo.
>>
>> It indicates the size offset of the memory region addressed by TTBR1_EL1
>
>> and hence can be used for determining the vabits_actual value.
>
> used for determining random-internal-kernel-variable, that might not exist tomorrow.
>
> Could you describe how this is useful/necessary if a debugger wants to walk the page
> tables from the core file? I think this is a better argument.
>
> Wouldn't the documentation be better as part of the patch that adds the export?
> (... unless these have to go via different trees? ..)

Ok, will fix the same in v6 version.

>> diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst
>> index 447b64314f56..f9349f9d3345 100644
>> --- a/Documentation/admin-guide/kdump/vmcoreinfo.rst
>> +++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst
>> @@ -398,6 +398,12 @@ KERNELOFFSET
>> The kernel randomization offset. Used to compute the page offset. If
>> KASLR is disabled, this value is zero.
>>
>> +TCR_EL1.T1SZ
>> +------------
>> +
>> +Indicates the size offset of the memory region addressed by TTBR1_EL1
>
>> +and hence can be used for determining the vabits_actual value.
>
> 'vabits_actual' may not exist when the next person comes to read this documentation (its
> going to rot really quickly).
>
> I think the first half of this text is enough to say what this is for. You should include
> words to the effect that its the hardware value that goes with swapper_pg_dir. You may
> want to point readers to the arm-arm for more details on what the value means.

Ok, got it. Fixed this in v6, which should be on its way shortly.

Thanks,
Bhupesh