Re: [PATCH 6/9] mm: convert PTE table entry to pte

[Alexander Gordeev]

On Fri, Aug 07, 2026 at 05:26:04PM +0100, Muhammad Usama Anjum wrote:
> On 07/08/2026 7:58 am, Alexander Gordeev wrote:
> > On Thu, Aug 06, 2026 at 09:38:44AM +0100, Muhammad Usama Anjum wrote:
> >> The non-MMU stub receives hw_pte_t but returns a logical pte_t
> >> value. Convert the stored entry through __pte_from_hw() before
> >> returning.
> >>
> >> Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
> >> ---
> >>  include/linux/hugetlb.h | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> >> index bc0b9c65aa1d0..9e8b391aa4bc9 100644
> >> --- a/include/linux/hugetlb.h
> >> +++ b/include/linux/hugetlb.h
> >> @@ -1283,7 +1283,7 @@ static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
> >>  #ifdef CONFIG_MMU
> >>  	return ptep_get(ptep);
> >>  #else
> >> -	return *ptep;
> >> +	return __pte_from_hw(*ptep);
> > 
> > But this is a direct dereferencing, which breaks the whole point, isn't it?
> Yes, this is particular line is for non MMU. In this case, CONIFG_ARCH_HAS_HW_PTE
> would never be defined. Hence hw_pte_t is just pte_t and direct dereference is
> allowed. I'd thought a lot about it; is better to leave direct dereference here
> or use some helper. Then used __pte_from_hw() was already being used in generic
> ptep_get().

But in case CONIFG_ARCH_HAS_HW_PTE=n __pte_from_hw() is still gets called.
That looks inconsistent to me. Why not just call ptep_deref() (see below)?

> There are only two users of __pte_from_hw() at this time. 
> 
> > 
> > What about introducing something like pte_t ptep_get_sw(hw_pte_t *ptep)
> > to be used in exactly situations like this? With that the semantics of
> > hw_pte_t pointers becomes straightforward and closes the still ongoing
> > "storage vs lifetime" discussion:
> > 
> > hw_pte_t*     points to HW-formatted page table entries
> > 
> > ptep_get()    is used to obtain HW-linked/attached entries, and may wire
> >               extra code like [1] or [2]
> > 
> > ptep_get_sw() is used to obtain HW-unlinked/unattached entries and in
> >               most cases is just a direct dereference
> ptep_get_sw() or ptep_get_deref() is better name here?

ptep_deref() would be it.

Do you agree to the suggested API requirements?

> I thought __pte_from_hw() is ugly enough that if someone tries to use it
> wrongly, it'll be noticed pretty easily. I'm fine with any other name.

The name may be not perfect, but it is the way it is used above looks
wrong to me.

> > The caller should always know whether the entry is attached or not, so
> > confusions like [3] are avoided.
> > 
> > 1. https://lore.kernel.org/linux-mm/20260526-kpkeys-v8-21-eaaacdacc67c@xxxxxxx/
> > 2. https://lore.kernel.org/linux-s390/650903a4-0dd9-4e6b-9d4b-3c32c5657236-agordeev@xxxxxxxxxxxxx/
> > 3. https://lore.kernel.org/linux-s390/b44e071d-7c9d-4e7e-a84d-4af3499a5a05@xxxxxxx/
> > 
> >>  #endif
> >>  }

Thanks!

> -- 
> Thanks,
> Usama
>