I'm trying to wrap my head around any forward compatibility concerns... if we misidentify a fault as spurious that would be bad.
On May 15, 2014 1:50:13 PM PDT, Dave Hansen <[email protected]> wrote: >On 05/12/2014 03:29 AM, David Vrabel wrote: >> - /* Reserved-bit violation or user access to kernel space? */ >> - if (error_code & (PF_USER | PF_RSVD)) >> + /* Only check for spurious faults on supervisor write or >> + instruction faults. */ >> + if (error_code != (PF_WRITE | PF_PROT) >> + && error_code != (PF_INSTR | PF_PROT)) >> return 0; > >This changes the semantics a bit too much for me to feel happy about >it. > This is at best missing quite a bit of detail from the changelog. > > 1. 'return 0' means "this was not a spurious fault" > 2. We used to check for the presence of PF_USER|PF_RSVD > 3. This patch checks now for two _explicit_ conditions, which > implicitly check for the _absence_ of the two bits we checked for > before. > >I do believe your patch is correct, but it took me a bit to convince >myself that it was the right thing. Please be explicit (in the >comment) >about the exact PTE transitions that you expect to get you here. > >Also, I have to wonder if you can just leave the original if() in >there. > You're making this _more_ restrictive than it was before, and I wonder >if it might just be more clear if you have both checks. The compiler >might even compile it down to the same code, just changing the >immediate >that was generated for the mask that you're checking. -- Sent from my mobile phone. Please pardon brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
