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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 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 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A5BCB180009 X-Stat-Signature: 9xgxrxnogb8x78gfhhoz6tcs9karb7ze X-HE-Tag: 1789564998-111392 X-HE-Meta: U2FsdGVkX18XihjqrLfK8/g0nOgdETgRui/4ClUawlLIZwMp+UOvC9exKNq6HI4B3o85IT9ZVcy3cD8fePxHahLbEWOBHKFXd9SOAzjGfdisBg8cAl/wsbqtOxScSYVu/DTEjm0YBkmf32xtCePZL/ZMSWSFCX9aGM5dCzYP2GmpZ9wm+B/y2MWi/qSUA+Q2Y2kRLI+iz2BPQlx/+bkXH8RX15KwUQqzUGqlro6+C3XInPN/K96i8JZXuPcogU+V1ATv+qLinbk3CCVecpqk9n0G81ewan55Tn3UqLbPqNASdIHcVVt9wO9bDMq4Ft6OMEjne2sfNbi2ksUJ9RlPbhMuxwEtzdIM0EyutH5jqdKoRgFh1MXbk3/57fggnG8ycBc3KdhnjnA1CpguAb45nmqDnrTbBAIZJpEty15OvDVwtk5JICvT3LUnZZ/B6SJBfj2bwRTLCHvCnl0SifY6ttIXiJmPXwmNFVTfbnjHtg97PiJDuVF3rfIIdsLC2RU6iM5jxmbf3ZM0il7cYMTNVN5bK+XQQBFhdUEj9i1wF19hA57Y+tm4ofTeMQDLthjdMIo7zaPmsePZjQ9l0FM1V8OY6DqTBH2XC3zwGsKuiOmP6IvMR43VHhsUxZUCtzjf38ZvAlCzN+KtuRt+fB/0ETP12PyMnlAGNsUoGj2aT/vmFdKocspMgMqVV1CMJFMN4NWHVOpkpk0XxiDfyUq217MVRDJQFgxDOJgpyENweKAmdmmMBYOmt/bCBmL57Q8L6GSNjPiBqP2Fw3Kj0BCQwXWcia9zRrJjFchQkR3aKqNsfkuVAMv3Zlq8I/Mmt7hfkyalEu2nDZ6zFW9fntmgPg6sZQcO7Xr1NEKUyo8rR2hENImlPxK6sFUGBlEIDvI4lIhGNFbl0PgTKejrEqIk2iQbPnABPgJAzxhJPsuZVcxCH6t5A9Y2keLZb8RpfqsLBgxghniBINOPqBIU5ub a+tTu1rb 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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 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