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X-CSE-ConnectionGUID: sLzy7szsTCChQrx5O/CICA== X-CSE-MsgGUID: KrgT+ZKrRzajpN7ioSQx5w== X-IronPort-AV: E=McAfee;i="6700,10204,11336"; a="42231261" X-IronPort-AV: E=Sophos;i="6.13,263,1732608000"; d="scan'208";a="42231261" Received: from fmviesa007.fm.intel.com ([10.60.135.147]) by fmvoesa107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2025 16:57:15 -0800 X-CSE-ConnectionGUID: Ij/bjUBYSeCrQkzss4lIxg== X-CSE-MsgGUID: H5HXzbVLQDq891KmmFx/mQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.13,263,1732608000"; d="scan'208";a="110966239" Received: from aschofie-mobl2.amr.corp.intel.com (HELO [10.125.110.153]) ([10.125.110.153]) by fmviesa007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2025 16:57:13 -0800 Message-ID: Date: Wed, 5 Feb 2025 16:57:15 -0800 Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 08/15] x86: Physical address comparisons in fill_p*d/pte To: Maciej Wieczor-Retman , luto@kernel.org, xin@zytor.com, kirill.shutemov@linux.intel.com, palmer@dabbelt.com, tj@kernel.org, andreyknvl@gmail.com, brgerst@gmail.com, ardb@kernel.org, dave.hansen@linux.intel.com, jgross@suse.com, will@kernel.org, akpm@linux-foundation.org, arnd@arndb.de, corbet@lwn.net, dvyukov@google.com, richard.weiyang@gmail.com, ytcoode@gmail.com, tglx@linutronix.de, hpa@zytor.com, seanjc@google.com, paul.walmsley@sifive.com, aou@eecs.berkeley.edu, justinstitt@google.com, jason.andryuk@amd.com, glider@google.com, ubizjak@gmail.com, jannh@google.com, bhe@redhat.com, vincenzo.frascino@arm.com, rafael.j.wysocki@intel.com, ndesaulniers@google.com, mingo@redhat.com, catalin.marinas@arm.com, junichi.nomura@nec.com, nathan@kernel.org, ryabinin.a.a@gmail.com, dennis@kernel.org, bp@alien8.de, kevinloughlin@google.com, morbo@google.com, dan.j.williams@intel.com, julian.stecklina@cyberus-technology.de, peterz@infradead.org, cl@linux.com, kees@kernel.org Cc: kasan-dev@googlegroups.com, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, linux-doc@vger.kernel.org References: <2c2a71ec844db597f30754dd79faf87c9de0b21f.1738686764.git.maciej.wieczor-retman@intel.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 2/4/25 09:33, Maciej Wieczor-Retman wrote: > @@ -287,7 +287,7 @@ static pte_t *fill_pte(pmd_t *pmd, unsigned long vaddr) > if (pmd_none(*pmd)) { > pte_t *pte = (pte_t *) spp_getpage(); > pmd_populate_kernel(&init_mm, pmd, pte); > - if (pte != pte_offset_kernel(pmd, 0)) > + if (__pa(pte) != __pa(pte_offset_kernel(pmd, 0))) > printk(KERN_ERR "PAGETABLE BUG #03!\n"); > } > return pte_offset_kernel(pmd, vaddr); Maciej, could you do a quick check on this and make sure that it doesn't hurt code generation on current kernels? pte_offset_kernel() has an internal __va() so this ends up logically being something like: - if ( pte != __va(pmd)) + if (__pa(pte) != __pa(__va(pmd))) The __pa() and __va() obviously logically cancel each other out in the new version. But if the compiler for whatever reason can't figure this out we might end up with worse code. If it generates crummy code we might want to do this differently like avoiding pte_offset_kernel() and adding some other helper that's more direct and to the point.