Re: [PATCH 1/8] mm: Add ptep_try_set() for lockless empty-slot installs

[David Hildenbrand (Arm)]

On 6/14/26 22:29, Tejun Heo wrote:
> Hello,
> 
> On Sun, Jun 14, 2026 at 10:28:02AM +0100, Will Deacon wrote:
>>> +/*
>>> + * Note: strictly-zero compare is narrower than pte_none(), but the gap is
>>> + * harmless: a fresh kernel PTE has no software bits set.
>>> + */
>>
>> This comment really confused me :/
>>
>> What is a "fresh" kernel PTE and why do you specifically call out "software
>> bits" if the CAS requires all 64 bits to be 0? Why is that narrower than
>> pte_none() given that pte_none() for arm64 is:
>>
>> #define pte_none(pte)           (!pte_val(pte))
> 
> Yeah, that's complete non-sense for arm. The comment is about x86's
> pte_none() excluding DIRTY and ACCESSED due to an erratum when testing none
> and how that doesn't matter here. This shouldn't have been copied to arm.
> I'll send a patch to remove that.

Is BPF maybe picking up patches from other subsystems up too early without
waiting for acks?

-- 
Cheers,

David