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SubjectRe: [PATCH] x86/mm/fault: Streamline the fault error_code decoder some more
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> On Dec 6, 2018, at 8:47 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Andy Lutomirski <luto@amacapital.net> wrote:
>
>>> vs. (with SGX added as 'G' for testing purposes)
>>>
>>> [ 0.158849] #PF error code(0001): +P !W !U !S !I !K !G
>>> [ 0.159292] #PF error code(0003): +P +W !U !S !I !K !G
>>> [ 0.159742] #PF error code(0007): +P +W +U !S !I !K !G
>>> [ 0.160190] #PF error code(0025): +P !W +U !S !I +K !G
>>> [ 0.160638] #PF error code(0002): !P +W !U !S !I !K !G
>>> [ 0.161087] #PF error code(0004): !P !W +U !S !I !K !G
>>> [ 0.161538] #PF error code(0006): !P +W +U !S !I !K !G
>>> [ 0.161992] #PF error code(0014): !P !W +U !S +I !K !G
>>> [ 0.162450] #PF error code(0011): +P !W !U !S +I !K !G
>>> [ 0.162667] #PF error code(8001): +P !W !U !S !I !K +G
>>> [ 0.162667] #PF error code(8003): +P +W !U !S !I !K +G
>>> [ 0.162667] #PF error code(8007): +P +W +U !S !I !K +G
>>> [ 0.162667] #PF error code(8025): +P !W +U !S !I +K +G
>>> [ 0.162667] #PF error code(8002): !P +W !U !S !I !K +G
>>> [ 0.162667] #PF error code(8004): !P !W +U !S !I !K +G
>>> [ 0.162667] #PF error code(8006): !P +W +U !S !I !K +G
>>> [ 0.162667] #PF error code(8014): !P !W +U !S +I !K +G
>>> [ 0.162667] #PF error code(8011): +P !W !U !S +I !K +G
>>> [ 0.162667] #PF error code(0000): !P !W !U !S !I !K !G
>>>
>>
>> Please don’t. The whole reason I added the decoding was to make it easy
>> to read without a cheat sheet. This is incomprehensible without
>> reference to the code, and I’m familiar with it to begin with.
>
> Dunno, I can deduct the meaning from the above abbreviations without a
> cheat sheet and I'm sure you'll be able to too from now on. All the
> letters are very obvious references - to me at least, and brevity and
> predictable, fixed-length output matters.
>
>> How about:
>>
>> #PF error code: 0001 [PROT read kernel]
>>
>> #PF error code: 0001 [PROT WRITE kernel]
>>
>> #PF error code: 0001 [PROT read kernel]
>>
>> #PF error code: 8011 [PROT INSTR kernel SGX]
>>
>> This has no noise from unset bits except that we add lowercase “read”
>> or “kernel” as appropriate. Even “kernel” seems barely necessary.
>
> The thing is, the 'noise' from unset bits is actually important
> information as well - at least for the major bits: it was a mostly random
> choice that Intel defined '1' for write access and not for read access.
>
>

That’s why I suggested “read,” in lowercase, for reads. Other than that, most of the unset bits are uninteresting. An OOPS is so likely to be a kernel fault that it’s barely worth mentioning, and I even added a whole separate diagnostic for user oopses. Similarly, I don’t think we need to remind the reader that an oops wasn’t an SGX error or that it wasn’t a PK error. So I think my idea highlights the interesting bits and avoids distraction from the uninteresting bits.
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