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X-CSE-ConnectionGUID: vlIB1bxpTGuwl1IPlQ4LGA== X-CSE-MsgGUID: NJbx45gkTxScO1a11z3TfQ== X-IronPort-AV: E=McAfee;i="6800,10657,11529"; a="68697584" X-IronPort-AV: E=Sophos;i="6.17,309,1747724400"; d="scan'208";a="68697584" Received: from orviesa006.jf.intel.com ([10.64.159.146]) by fmvoesa105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Aug 2025 10:36:14 -0700 X-CSE-ConnectionGUID: OeJWtaQ9Sf2wv3oMHTrZHw== X-CSE-MsgGUID: 3zh/WxAMSy6zdBECMmBLcA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.17,309,1747724400"; d="scan'208";a="167700499" Received: from puneetse-mobl.amr.corp.intel.com (HELO [10.125.108.119]) ([10.125.108.119]) by orviesa006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Aug 2025 10:36:14 -0700 Message-ID: <3976ef5d-a959-408a-b538-7feba1f0ab7a@intel.com> Date: Thu, 21 Aug 2025 10:36:12 -0700 Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: fix KASAN build error due to p*d_populate_kernel() To: Harry Yoo Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, andreyknvl@gmail.com, aneesh.kumar@linux.ibm.com, anshuman.khandual@arm.com, apopple@nvidia.com, ardb@kernel.org, arnd@arndb.de, bp@alien8.de, cl@gentwo.org, dave.hansen@linux.intel.com, david@redhat.com, dennis@kernel.org, dev.jain@arm.com, dvyukov@google.com, glider@google.com, gwan-gyeong.mun@intel.com, hpa@zyccr.com, jane.chu@oracle.com, jgross@suse.de, jhubbard@nvidia.com, joao.m.martins@oracle.com, joro@8bytes.org, kas@kernel.org, kevin.brodsky@arm.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, luto@kernel.org, maobibo@loongson.cn, mhocko@suse.com, mingo@redhat.com, osalvador@suse.de, peterx@redhat.com, peterz@infradead.org, rppt@kernel.org, ryabinin.a.a@gmail.com, ryan.roberts@arm.com, stable@vger.kernel.org, surenb@google.com, tglx@linutronix.de, thuth@redhat.com, tj@kernel.org, urezki@gmail.com, vbabka@suse.cz, vincenzo.frascino@arm.com, x86@kernel.org, zhengqi.arch@bytedance.com References: <20250821093542.37844-1-harry.yoo@oracle.com> <20250821115731.137284-1-harry.yoo@oracle.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/21/25 04:57, Harry Yoo wrote: > However, {pgd,p4d}_populate_kernel() is defined as a function regardless > of the number of page table levels, so the compiler may not optimize > them away. In this case, the following linker error occurs: This part of the changelog confused me. I think it's focusing on the wrong thing. The code that's triggering this is literally: > pgd_populate(&init_mm, pgd, > lm_alias(kasan_early_shadow_p4d)); It sure _looks_ like it's unconditionally referencing the 'kasan_early_shadow_p4d' symbol. I think it's wrong to hide that with macro magic and just assume that the macros won't reference it. If a symbol isn't being defined, it shouldn't be referenced in C code.:q The right way to do it is to have an #ifdef in a header that avoids compiling in the reference to the symbol. But just changing the 'static inline' to a #define seems like a fragile hack to me.