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h=Date:From:To:Cc:Subject:References:In-Reply-To; b=jlLD6yuFDosHEmd6JzFv/rPZm04Jd/L0IencJCYXxb65CisXMkNidUNhwaDOZsD5p cM7KEQ8mbz1fxDWDQPDd02HLkioIVNmVIPX+9pme9NckO9RuD92oU52O33Y/0rLS5L yp23VOHR8uJX3zOEqKf+Sst8wyQEgidw7WkMwhPW6M+bNXp8YU+/ztMXgqkpCIvvuv +33wxUGO31GXBEGLK/j8nNTVK5CNaJsu61ffdl4mKBVty8Vv+K//kufvTaJ+E9+yfh eFanxfBigamyNqn/1TCCvEiMOw4MINMe4k4fnxLc31nAxIeYFCX/Cb5czHSrTIsVzZ hlJfasBj+UcZQ== Date: Wed, 16 Sep 2026 14:41:34 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Anshuman Khandual , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Andrew Morton , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Lorenzo Stoakes Subject: Re: [PATCH V2 01/14] mm: Add read-write accessors for vm_page_prot Message-ID: References: <20260907035030.2839978-1-anshuman.khandual@arm.com> <20260907035030.2839978-2-anshuman.khandual@arm.com> <69a7987f-15fb-4793-81b6-cc436525224e@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69a7987f-15fb-4793-81b6-cc436525224e@kernel.org> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: B0C89140004 X-Rspam-User: X-Stat-Signature: 3boocgxbmtuadhcyc14id4dm474d9u5a X-HE-Tag: 1789566101-977421 X-HE-Meta: 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 MZt+h4IQ 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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 Wed, Sep 16, 2026 at 03:23:13PM +0200, David Hildenbrand (Arm) wrote: > 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(). Yes please! :) > > 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 -- Cheers, Lorenzo