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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=J8sN6vHT6wwFlL7w+ibtbyy+RquT3UJgu31Rqk6lPgGMfOEtwfVy0CDOl0+tf2hL+ P+5722EfEjo8+QgJZlfBEyhlP2lqjI1tiMA8hoLKpVioc1QG7k/fkkQDQpBfWRMEwE TiXiGNaYeB1yOH41Pu6Vrltn9LQFfwVlfj8zKXSQ= Message-ID: <1267a6c0-f8e7-4708-96da-4d131b5c6069@arm.com> Date: Tue, 7 Apr 2026 08:58:46 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] perf/events: Replace READ_ONCE() with standard pgtable accessors To: linux-mm@kvack.org, Andrew Morton , David Hildenbrand Cc: Andrew Morton , David Hildenbrand , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260227062744.2215491-1-anshuman.khandual@arm.com> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <20260227062744.2215491-1-anshuman.khandual@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: g5myogyn8zcue11suxoj9jn8jzmmsqwu X-Rspamd-Queue-Id: 6A20640006 X-Rspamd-Server: rspam09 X-HE-Tag: 1775532534-421646 X-HE-Meta: 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 Jk9fPgYU 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27/02/26 11:57 AM, Anshuman Khandual wrote: > Replace raw READ_ONCE() dereferences of pgtable entries with corresponding > standard page table accessors pxdp_get() in perf_get_pgtable_size(). These > accessors default to READ_ONCE() on platforms that don't override them. So > there is no functional change on such platforms. > > However arm64 platform is being extended to support 128 bit page tables via > a new architecture feature i.e FEAT_D128 in which case READ_ONCE() will not > provide required single copy atomic access for 128 bit page table entries. > Although pxdp_get() accessors can later be overridden on arm64 platform to > extend required single copy atomicity support on 128 bit entries. > > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Arnaldo Carvalho de Melo > Cc: Namhyung Kim > Cc: linux-perf-users@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Acked-by: Peter Zijlstra (Intel) > Signed-off-by: Anshuman Khandual > --- > This patch applies both on v7.0-rc1 and mm-unstable. > > Part of the D128 series but independent. Hence could be considered on its own. > > https://lore.kernel.org/all/20260224051153.3150613-5-anshuman.khandual@arm.com/ > > Collected Peter's tag from an off list conversation. Gentle ping. Still don't see this patch in latest next-20260406. Hence just wondering which tree and branch this patch is being picked up ? Thank you - Anshuman > > kernel/events/core.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index ac70d68217b6..4ee151cd2c6d 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -8422,7 +8422,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr) > pte_t *ptep, pte; > > pgdp = pgd_offset(mm, addr); > - pgd = READ_ONCE(*pgdp); > + pgd = pgdp_get(pgdp); > if (pgd_none(pgd)) > return 0; > > @@ -8430,7 +8430,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr) > return pgd_leaf_size(pgd); > > p4dp = p4d_offset_lockless(pgdp, pgd, addr); > - p4d = READ_ONCE(*p4dp); > + p4d = p4dp_get(p4dp); > if (!p4d_present(p4d)) > return 0; > > @@ -8438,7 +8438,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr) > return p4d_leaf_size(p4d); > > pudp = pud_offset_lockless(p4dp, p4d, addr); > - pud = READ_ONCE(*pudp); > + pud = pudp_get(pudp); > if (!pud_present(pud)) > return 0; >