Re: [PATCH v2 2/5] mm: add PTE_MARKER_GUARD PTE marker

[Dave Hansen]

On 10/21/24 14:13, Lorenzo Stoakes wrote:
>> Do you think there's enough value int his to warrant digging in? And indeed
>> I imagine bits are in short supply for this and would need a strong
>> argument to get... so yeah I don't think too worthwhile most likely!
>>
>> Thanks for the suggestion though!
> To put it on list - Dave Hansen commented on IRC that it would be safer to
> avoid this for now due to this being an ABI change, and reasonable to
> perhaps add it later if required, so that seems a sensible way forward.

We added SEGV_PKUERR because we really did expect signal handlers to
want to do something new and special, including consuming si_pkey.  Old
signal handlers would probably be pretty confused.

So, yeah, if it's not crystal clear that new signal handler code is
needed, than I'd punt on adding a new SEGV_* code for now.

BTW, SEGV_* codes are sequentially assigned.  It isn't a bitfield and
there are no space constraints.  We've only used a dozen or so of them
and ->si_code is an int.