[PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag

[Will Deacon]

On Mon, Jan 11, 2021 at 11:25:37AM -0800, Linus Torvalds wrote:
> On Mon, Jan 11, 2021 at 6:24 AM Kirill A. Shutemov <kirill at shutemov.name> wrote:
> >
> > I wonder if it would be acceptable to pass down to faultaround a copy
> > of vmf, so it mess with it without risking to corrupt the original one?
> 
> I'd almost prefer to split vmf into two parts: the 'this is the fault
> info' part and the 'this is the fault handling state' part.
> 
> So the first one would be filled in by the actual page faulter (or
> GUP) - and then be 'const' during the lookup, while the second one
> would be set up by handle_mm_fault() and would contain that "this is
> the current state of my fault state machine" and contain things like
> that ->pte thing.
> 
> And then if somebody actually needs to pass in "modified fault state"
> (ie that whole "I'm doing fault-around, so I'll use multiple
> addresses") they'd never modify the address in the fault info, they'd
> just pass the address as an explicit argument (like most cases already
> do - the "change addr or flags in vmf" is actually already _fairly_
> rare).

Alright then, I'll take another crack at this for v3 and see how far I
get.

Will