Re: [PATCH] x86/mm/fault: Streamline the fault error_code decoder some more

[Ingo Molnar <mingo@kernel.org>]

* 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. 

Thanks,

	Ingo