From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Tejun Heo <tj@kernel.org>, Will Deacon <will@kernel.org>
Cc: David Vernet <void@manifault.com>,
Andrea Righi <arighi@nvidia.com>,
Changwoo Min <changwoo@igalia.com>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <martin.lau@linux.dev>,
Kumar Kartikeya Dwivedi <memxor@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@kernel.org>,
Emil Tsalapatis <emil@etsalapatis.com>,
sched-ext@lists.linux.dev, bpf@vger.kernel.org, x86@kernel.org,
linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/8] mm: Add ptep_try_set() for lockless empty-slot installs
Date: Mon, 15 Jun 2026 13:49:18 +0200 [thread overview]
Message-ID: <f6e87467-2fa1-4edc-a739-9899be36196c@kernel.org> (raw)
In-Reply-To: <ai8PO0NThJeuQYzy@slm.duckdns.org>
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
next prev parent reply other threads:[~2026-06-15 11:49 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-22 17:22 [PATCHSET v4 sched_ext/for-7.2] bpf/arena: Direct kernel-side access Tejun Heo
2026-05-22 17:22 ` [PATCH 1/8] mm: Add ptep_try_set() for lockless empty-slot installs Tejun Heo
2026-05-22 22:07 ` David Hildenbrand (Arm)
2026-05-25 15:50 ` patchwork-bot+netdevbpf
2026-06-14 9:28 ` Will Deacon
2026-06-14 20:29 ` Tejun Heo
2026-06-15 11:49 ` David Hildenbrand (Arm) [this message]
2026-06-15 16:27 ` Tejun Heo
2026-06-15 17:36 ` David Hildenbrand (Arm)
2026-06-15 17:40 ` Tejun Heo
2026-05-22 17:22 ` [PATCH 2/8] bpf: Recover arena kernel faults with scratch page Tejun Heo
2026-05-26 12:45 ` David Hildenbrand (Arm)
2026-05-28 21:30 ` Alexei Starovoitov
2026-05-29 18:12 ` Tejun Heo
2026-05-29 18:38 ` Alexei Starovoitov
2026-05-29 18:44 ` Tejun Heo
2026-05-31 17:47 ` Tejun Heo
2026-05-31 18:58 ` David Hildenbrand (Arm)
2026-06-01 0:16 ` Alexei Starovoitov
2026-05-22 17:22 ` [PATCH 3/8] bpf: Add sleepable variant of bpf_arena_alloc_pages for kernel callers Tejun Heo
2026-05-22 17:22 ` [PATCH 4/8] bpf: Add bpf_struct_ops_for_each_prog() Tejun Heo
2026-05-22 17:22 ` [PATCH 5/8] bpf/arena: Add bpf_arena_map_kern_vm_start() and bpf_prog_arena() Tejun Heo
2026-05-22 17:22 ` [PATCH 6/8] sched_ext: Require an arena for cid-form schedulers Tejun Heo
2026-05-22 17:22 ` [PATCH 7/8] sched_ext: Sub-allocator over kernel-claimed BPF arena pages Tejun Heo
2026-05-22 17:22 ` [PATCH 8/8] sched_ext: Convert ops.set_cmask() to arena-resident cmask Tejun Heo
2026-05-25 15:45 ` [PATCHSET v4 sched_ext/for-7.2] bpf/arena: Direct kernel-side access Alexei Starovoitov
2026-05-25 19:54 ` Tejun Heo
-- strict thread matches above, loose matches on Subject: below --
2026-05-20 23:50 [PATCHSET v3 " Tejun Heo
2026-05-20 23:50 ` [PATCH 1/8] mm: Add ptep_try_set() for lockless empty-slot installs Tejun Heo
2026-05-21 7:00 ` Andrea Righi
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