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X-IronPort-AV: E=McAfee;i="6600,9927,10897"; a="4399633" X-IronPort-AV: E=Sophos;i="6.04,206,1695711600"; d="scan'208";a="4399633" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmvoesa102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Nov 2023 07:19:15 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10897"; a="765656637" X-IronPort-AV: E=Sophos;i="6.04,206,1695711600"; d="scan'208";a="765656637" Received: from phelpsmi-mobl2.amr.corp.intel.com (HELO [10.212.139.180]) ([10.212.139.180]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Nov 2023 07:19:14 -0800 Message-ID: <3ff3e05a-8377-4b38-84ae-be24b6cae6a4@intel.com> Date: Fri, 17 Nov 2023 07:19:12 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86: Fixes warning: cast removes address space '__user' of expression in uaccess_64.h Content-Language: en-US To: Dipendra Khadka , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com Cc: mjguzik@gmail.com, ira.weiny@intel.com, linux-kernel@vger.kernel.org References: <20231116173849.210205-1-kdipendra88@gmail.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-0.9 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on agentk.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (agentk.vger.email [0.0.0.0]); Fri, 17 Nov 2023 07:19:29 -0800 (PST) On 11/16/23 09:38, Dipendra Khadka wrote: > Sparse has identified a warning as follows: > > ./arch/x86/include/asm/uaccess_64.h:88:24: warning: cast removes address space '__user' of expression. > > Since the valid_user_address(x) macro implicitly casts the argument > to long and compares the converted value of x to zero, casting ptr > to unsigned long has no functional impact and does not trigger a > Sparse warning either. Why does sparse complain about a cast to 'long' but not 'unsigned long'? Both remove the '__user' address space from the expression. Were there just so many __user pointers being cast to 'unsigned long' that there's an exception in sparse for 'void __user *' => 'unsigned long'? Either way, if we're going to fix it it seems like it would be better to valid_user_address() actually handle, well, __user addresses rather than expecting callers to do it.