[PATCH v3 06/22] mm: Always use page table accessor functions

[Lorenzo Stoakes]

On Wed, Nov 26, 2025 at 03:56:13PM +0100, David Hildenbrand (Red Hat) wrote:
> On 11/26/25 15:52, Lorenzo Stoakes wrote:
> >
> > Would the pmdp_get() never get invoked then? Or otherwise wouldn't that end up
> > requiring a READ_ONCE() further up the stack?
>
> See my other reply, I think the pmdp_get() is required because all pud_*
> functions are just simple stubs.

OK, thought you were saying we should push further down the stack? Or up
depending on how you view these things :P as in READ_ONCE at leaf?

Anyway. I am now designating you the expert at this ;)

>
> >
> > >
> > > IOW, push the READ_ONCE() down to the lowest level so the previous ones
> > > (that will get essentially ignore?) will get folded into the last
> > > READ_ONCE()?
> > >
> > > But my head still hurts and I am focusing on something else concurrently :)
> >
> > Even if we could make this work, I don't love that there's some implicit
> > assumption there that could easily break later on.
> >
> > I'd rather we kept it as stupid/obvious as possible...
>
> Looking at include/asm-generic/pgtable-nopmd.h I am not sure we are talking
> about implicit assumptions here. It's kind-of the design that the pud_t
> values are dummies, so why shoul the pudp_get() give you any guarantees.
>
> At least that's my current understanding, which might be very flawed :)

I mean I'm waving my hands around like I'm working on an aircraft carrier here
so if you're _sure_ it's _absolutely_ safe then fine :)

In other words - well volunteered, sir ;)

>
> --
> Cheers
>
> David
>
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Cheers, Lorenzo