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s=arc-20220608; d=hostedemail.com; t=1726223136; a=rsa-sha256; cv=none; b=TUO+s/nj0hOWe6Rv5BF/O0obe6KTvHvr5gtfygQUZVikkH63eqfzmkq0S5/NzhuKNQdoju GRRP2SCGKQYkV0kk/wWTaZ4bYJ7CEXpq8ur1UWjRvbz6Ova1zRNncJWe2aKdwlPZaNL3iB h876SCHCIDxk+QXOo0yfTzF5oH6iOoI= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf30.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 372AA13D5; Fri, 13 Sep 2024 03:28:02 -0700 (PDT) Received: from [10.57.82.141] (unknown [10.57.82.141]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F132B3F64C; Fri, 13 Sep 2024 03:27:30 -0700 (PDT) Message-ID: Date: Fri, 13 Sep 2024 11:27:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/7] mm: Use ptep_get() for accessing PTE entries To: Anshuman Khandual , linux-mm@kvack.org Cc: Andrew Morton , David Hildenbrand , "Mike Rapoport (IBM)" , Arnd Bergmann , x86@kernel.org, linux-m68k@lists.linux-m68k.org, linux-fsdevel@vger.kernel.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org References: <20240913084433.1016256-1-anshuman.khandual@arm.com> <20240913084433.1016256-4-anshuman.khandual@arm.com> Content-Language: en-GB From: Ryan Roberts In-Reply-To: <20240913084433.1016256-4-anshuman.khandual@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: C2CFB8000E X-Stat-Signature: 9arncf5usre7unc4grgy1ducunm79mci X-Rspam-User: X-HE-Tag: 1726223253-449941 X-HE-Meta: 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 CRUOAOKG jbrXkWinFFSB1BMCTi2WrSajyn7oVqK+sJpI38D7o/JpfXUKflVZFa6qFUKdqQZA6CWTFhSJVRvfOHbMBzb/TqlhIAdjk6orv6TWkOU3z4acOHJ+Bgv4HLFMeN8JnG4kkXRR9fKhsKLbXmftPoXdYKnc3z3ZPK1GCh/ODj5fqXbZRDwJDh1af2WcaC746iQtvvy/rkAI+RzUexVogCL1YvCMu3+xDBaPqY7fijR50/EHG9oI3IKczowtNRGxpBl0NNyU6pEq1zHzA9dQqTRzwjVlPhhZ10GEndilC76fwIG5U0AQnvAmGcx+BxcyWbg+mEoy9evt2E1g5AiF0D1ybkA8QNOoagcePuAwm+uSYE4G6ctXOp2K9uMvCTUAI8nu29dznLTwO/IRCHjGJ1DY6DxEuChptPFupOvy2WqH5CWP54el4D/Xf4WXXVD1lvDKO80Vz X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 13/09/2024 09:44, Anshuman Khandual wrote: > Convert PTE accesses via ptep_get() helper that defaults as READ_ONCE() but > also provides the platform an opportunity to override when required. > > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Ryan Roberts > Cc: "Mike Rapoport (IBM)" > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual > --- > include/linux/pgtable.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index 2a6a3cccfc36..05e6995c1b93 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -1060,7 +1060,7 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b) > */ > #define set_pte_safe(ptep, pte) \ > ({ \ > - WARN_ON_ONCE(pte_present(*ptep) && !pte_same(*ptep, pte)); \ > + WARN_ON_ONCE(pte_present(ptep_get(ptep)) && !pte_same(ptep_get(ptep), pte)); \ Suggest reading once into a temporary so that the pte can't change between the 2 gets. In practice, it's not likely to be a huge problem for this instance since its under the PTL so can only be racing with HW update of access and dirty. But good practice IMHO: pte_t __old = ptep_get(ptep); \ WARN_ON_ONCE(pte_present(__old) && !pte_same(__old, pte)); \ Thanks, Ryan > set_pte(ptep, pte); \ > }) >