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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=bjxI+aQ8zFM9SyTQFzyGuKMzJg2y75xsC8VOiuWuEm99z0f5vvZn0tIA7wR7+h4Iy CzNTVCPduKNC02eWJmFtnGR1w9MZ9FUvS9hdN6XbJhkRIfwFDfcxyUx3QXbrABvHxb FKKbokiyNtbnCQKEVUV+bW6T2cZvHRUFw5fAnldY= Message-ID: <8ae905bd-fb1c-408d-bf50-77667a51e3a1@arm.com> Date: Fri, 10 Apr 2026 09:59:06 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC V1 02/16] mm: Add read-write accessors for vm_page_prot To: Mike Rapoport Cc: linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Lorenzo Stoakes , Andrew Morton , David Hildenbrand , Linu Cherian , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260224051153.3150613-1-anshuman.khandual@arm.com> <20260224051153.3150613-3-anshuman.khandual@arm.com> Content-Language: en-US From: Anshuman Khandual In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 1F20640008 X-Stat-Signature: w8u3fjt5zaesnkoj3gk8pc9cm5gzjntk X-HE-Tag: 1775795354-840888 X-HE-Meta: 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 JwgcA+cf 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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 09/04/26 4:07 PM, Mike Rapoport wrote: > Hi Anshuman, > > On Tue, Feb 24, 2026 at 10:41:39AM +0530, Anshuman Khandual wrote: >> Currently vma->vm_page_prot is safely read from and written to, without any >> locks with READ_ONCE() and WRITE_ONCE(). But with introduction of D128 page >> tables on arm64 platform, vm_page_prot grows to 128 bits which can't safely >> be handled with READ_ONCE() and WRITE_ONCE(). >> >> Add read and write accessors for vm_page_prot like pgprot_read/write_once() >> which any platform can override when required, although still defaulting as >> READ_ONCE() and WRITE_ONCE(), thus preserving the functionality for others. >> >> Cc: Andrew Morton >> Cc: David Hildenbrand >> Cc: Lorenzo Stoakes >> Cc: Mike Rapoport >> Cc: linux-mm@kvack.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Anshuman Khandual >> --- >> include/linux/pgtable.h | 14 ++++++++++++++ >> mm/huge_memory.c | 4 ++-- >> mm/memory.c | 2 +- >> mm/migrate.c | 2 +- >> mm/mmap.c | 2 +- >> 5 files changed, 19 insertions(+), 5 deletions(-) >> >> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h >> index da17139a1279..8858b8b03a02 100644 >> --- a/include/linux/pgtable.h >> +++ b/include/linux/pgtable.h >> @@ -495,6 +495,20 @@ static inline pgd_t pgdp_get(pgd_t *pgdp) >> } >> #endif >> >> +#ifndef pgprot_read_once >> +static inline pgprot_t pgprot_read_once(pgprot_t *prot) > > I don't think we need _once in the helper name. Presence of the helper > already implies that pointer should not be just dereferenced from one side > and that using the helper will do The Right Thing from the other side. Makes sense - will drop __once from the helper name.