From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7DD4637FF67 for ; Wed, 16 Sep 2026 13:23:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789565001; cv=none; b=LHFGIi6sDUfIcSzaUTnqDuG0G+ut9KDfHx4SGfz8eRZHImxk0qBi0zwQpRIEOMiyD5HjqX1j7bjYwtqNz8CuLtyZyJGwH2kP+5lCz7vq/rR7D8xrcpqKYO/eT9F1m6Molop2zdABF5d1Qn8+ng7fDtF78nlkjFyFf/76at9v5aI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789565001; c=relaxed/simple; bh=jsSn/dJ3du8mtrFnVq7nUxNuhYUF1hfGYrdD52t/hQA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=vBM/gluW8LWs0sPfEDVBbpjqRo2tPoTAp4HDZ4CLnCPLmnGLro1ZOHWi++CrORHcutppYI0vKqlo4fWf7PcNqkCz2pQsUkMQeLOPwaj/q9LjEzey2q5ddNQpVF1l44og6wHPsjdVvfsOevmZrBaxJzRvnWYdQBiTW7GbxlZiecw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iyqfQ56R; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iyqfQ56R" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7E2A01F000FF; Wed, 16 Sep 2026 13:23:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789564998; bh=t1n21esTWFIARb22DabL327mvFBcDYA8LulYh58X1JM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=iyqfQ56RCSKneDh03pMqIw3w4xWZI6hlxEMUUXydQndV49m08vRmeRcTuK5Ef+WjO o9QTFocyfQEIerKgrSC3l9RQGmjvcP7quw6zXK6TDxv+tr+tGyrXLlnRm8CHnm3ts+ tZvsitIFUR7yj7H2xjQR3atAhMD4MMwUeaYpSbFJr1tTo5hnQ/mJwAMDS0kIW9DA4Y smXDfOHMOFBUa+BqOm7WKQrGUCUIWZb4o1HXfMHnzR4W/Arupulis00Ym4dCVjWJOG sUb/pChJrOO216PGv0ZVv3oiEsr/qZPi8j5QkjKCq8XIJ2IYqoCb8aVDZiELS49uiE TLZchf3Rqv8Xw== Message-ID: <69a7987f-15fb-4793-81b6-cc436525224e@kernel.org> Date: Wed, 16 Sep 2026 15:23:13 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2 01/14] mm: Add read-write accessors for vm_page_prot To: Anshuman Khandual , linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Lorenzo Stoakes , Andrew Morton , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Lorenzo Stoakes References: <20260907035030.2839978-1-anshuman.khandual@arm.com> <20260907035030.2839978-2-anshuman.khandual@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/7/26 05:50, 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]() > 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 > Acked-by: Mike Rapoport (Microsoft) > 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 e3c8ab96941c..0df57a5c19ef 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -524,6 +524,20 @@ static inline pgd_t pgdp_get(pgd_t *pgdp) > } > #endif > > +#ifndef pgprot_read > +static inline pgprot_t pgprot_read(pgprot_t *prot) Try passing "const pgprot_t *prot" instead. [...] > diff --git a/mm/migrate.c b/mm/migrate.c > index 15b45832bcfa..579152cce502 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -387,7 +387,7 @@ static bool remove_migration_pte(struct folio *folio, > > folio_get(folio); > new = folio_page(folio, idx); > - pte = mk_pte(new, READ_ONCE(vma->vm_page_prot)); > + pte = mk_pte(new, pgprot_read(&vma->vm_page_prot)); I do wonder whether a ogprot_t vma_get_page_prot(const struct vm_area_struct *vma) where we hide the pgprot access would be a good complement for vma_set_page_prot(). Just a thought. > diff --git a/mm/mmap.c b/mm/mmap.c > index 4bf26b0f1e6e..729bc244b317 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -89,7 +89,7 @@ void vma_set_page_prot(struct vm_area_struct *vma) > vm_page_prot = vma_pgprot_modify(vm_page_prot, vma_flags); > } > /* remove_protection_ptes reads vma->vm_page_prot without mmap_lock */ > - WRITE_ONCE(vma->vm_page_prot, vm_page_prot); > + pgprot_write(&vma->vm_page_prot, vm_page_prot); > } > > /* -- Cheers, David