linux-kernel - arch/mips/mm/tlbex.c:2599 check_pabits() warn: always true condition '(fillbits >= ((__builtin_constant_p(0)) < 2) - __builtin

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Message-ID: <202103051337.i8Vifby3-lkp@intel.com>
Date:   Fri, 5 Mar 2021 13:32:44 +0800
From:   kernel test robot <lkp@...el.com>
To:     Jakub Jelinek <jakub@...hat.com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: arch/mips/mm/tlbex.c:2599 check_pabits() warn: always true condition
 '(fillbits >= ((__builtin_constant_p(0)) < 2) - __builtin_clzll(0)):((4 <=
 4)) => (0-u32max >= 0)'

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   280d542f6ffac0e6d65dc267f92191d509b13b64
commit: 2f78788b55baa3410b1ec91a576286abe1ad4d6a ilog2: improve ilog2 for constant arguments
date:   3 months ago
config: mips-randconfig-m031-20210305 (attached as .config)
compiler: mips64-linux-gcc (GCC) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@...el.com>

smatch warnings:
arch/mips/mm/tlbex.c:2599 check_pabits() warn: always true condition '(fillbits >= ((__builtin_constant_p(0)) ?(((0) < 2) ?0:63 - __builtin_clzll(0)):((4 <= 4)) ?__ilog2_u32(0):__ilog2_u64(0))) => (0-u32max >= 0)'

vim +2599 arch/mips/mm/tlbex.c

c5b367835cfc7a Steven J. Hill 2015-02-26  2569  
00bf1c691d082c Paul Burton    2015-09-22  2570  static void check_pabits(void)
00bf1c691d082c Paul Burton    2015-09-22  2571  {
00bf1c691d082c Paul Burton    2015-09-22  2572  	unsigned long entry;
00bf1c691d082c Paul Burton    2015-09-22  2573  	unsigned pabits, fillbits;
00bf1c691d082c Paul Burton    2015-09-22  2574  
00bf1c691d082c Paul Burton    2015-09-22  2575  	if (!cpu_has_rixi || !_PAGE_NO_EXEC) {
00bf1c691d082c Paul Burton    2015-09-22  2576  		/*
00bf1c691d082c Paul Burton    2015-09-22  2577  		 * We'll only be making use of the fact that we can rotate bits
00bf1c691d082c Paul Burton    2015-09-22  2578  		 * into the fill if the CPU supports RIXI, so don't bother
00bf1c691d082c Paul Burton    2015-09-22  2579  		 * probing this for CPUs which don't.
00bf1c691d082c Paul Burton    2015-09-22  2580  		 */
00bf1c691d082c Paul Burton    2015-09-22  2581  		return;
00bf1c691d082c Paul Burton    2015-09-22  2582  	}
00bf1c691d082c Paul Burton    2015-09-22  2583  
00bf1c691d082c Paul Burton    2015-09-22  2584  	write_c0_entrylo0(~0ul);
00bf1c691d082c Paul Burton    2015-09-22  2585  	back_to_back_c0_hazard();
00bf1c691d082c Paul Burton    2015-09-22  2586  	entry = read_c0_entrylo0();
00bf1c691d082c Paul Burton    2015-09-22  2587  
00bf1c691d082c Paul Burton    2015-09-22  2588  	/* clear all non-PFN bits */
00bf1c691d082c Paul Burton    2015-09-22  2589  	entry &= ~((1 << MIPS_ENTRYLO_PFN_SHIFT) - 1);
00bf1c691d082c Paul Burton    2015-09-22  2590  	entry &= ~(MIPS_ENTRYLO_RI | MIPS_ENTRYLO_XI);
00bf1c691d082c Paul Burton    2015-09-22  2591  
00bf1c691d082c Paul Burton    2015-09-22  2592  	/* find a lower bound on PABITS, and upper bound on fill bits */
00bf1c691d082c Paul Burton    2015-09-22  2593  	pabits = fls_long(entry) + 6;
00bf1c691d082c Paul Burton    2015-09-22  2594  	fillbits = max_t(int, (int)BITS_PER_LONG - pabits, 0);
00bf1c691d082c Paul Burton    2015-09-22  2595  
00bf1c691d082c Paul Burton    2015-09-22  2596  	/* minus the RI & XI bits */
00bf1c691d082c Paul Burton    2015-09-22  2597  	fillbits -= min_t(unsigned, fillbits, 2);
00bf1c691d082c Paul Burton    2015-09-22  2598  
00bf1c691d082c Paul Burton    2015-09-22 @2599  	if (fillbits >= ilog2(_PAGE_NO_EXEC))
00bf1c691d082c Paul Burton    2015-09-22  2600  		fill_includes_sw_bits = true;
00bf1c691d082c Paul Burton    2015-09-22  2601  
00bf1c691d082c Paul Burton    2015-09-22  2602  	pr_debug("Entry* registers contain %u fill bits\n", fillbits);
00bf1c691d082c Paul Burton    2015-09-22  2603  }
00bf1c691d082c Paul Burton    2015-09-22  2604  

:::::: The code at line 2599 was first introduced by commit
:::::: 00bf1c691d082c1945fdba032c03a9a82e9e7e61 MIPS: tlbex: Avoid placing software PTE bits in Entry* PFN fields

:::::: TO: Paul Burton <paul.burton@...tec.com>
:::::: CC: Ralf Baechle <ralf@...ux-mips.org>

---
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