Re: arch/m68k/include/asm/mmu_context.h:164 load_ksp_mmu() warn: unsigned 'mmuar' is never less than zero.
From: Hugh Dickins
Date: Thu Jul 06 2023 - 16:29:04 EST
Hi Geert,
On Thu, 6 Jul 2023, kernel test robot wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head: c17414a273b81fe4e34e11d69fc30cc8b1431614
> commit: e67b37c368b7cc24b8c0fe5ab6c44422312eab37 m68k: allow pte_offset_map[_lock]() to fail
> date: 2 weeks ago
> config: m68k-randconfig-m031-20230706 (https://download.01.org/0day-ci/archive/20230706/202307061849.rJKwVbXb-lkp@xxxxxxxxx/config)
> compiler: m68k-linux-gcc (GCC) 12.3.0
> reproduce: (https://download.01.org/0day-ci/archive/20230706/202307061849.rJKwVbXb-lkp@xxxxxxxxx/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202307061849.rJKwVbXb-lkp@xxxxxxxxx/
>
> New smatch warnings:
> arch/m68k/include/asm/mmu_context.h:164 load_ksp_mmu() warn: unsigned 'mmuar' is never less than zero.
>
> Old smatch warnings:
> arch/m68k/include/asm/mmu_context.h:114 load_ksp_mmu() warn: always true condition '(mmuar >= (0)) => (0-u32max >= 0)'
> arch/m68k/include/asm/mmu_context.h:140 load_ksp_mmu() warn: always true condition '(mmuar >= (0)) => (0-u32max >= 0)'
>
> vim +/mmuar +164 arch/m68k/include/asm/mmu_context.h
>
> 92
> 93 static inline void load_ksp_mmu(struct task_struct *task)
> 94 {
> 95 unsigned long flags;
> 96 struct mm_struct *mm;
> 97 int asid;
> 98 pgd_t *pgd;
> 99 p4d_t *p4d;
> 100 pud_t *pud;
> 101 pmd_t *pmd;
> 102 pte_t *pte = NULL;
> 103 unsigned long mmuar;
> 104
> 105 local_irq_save(flags);
> 106 mmuar = task->thread.ksp;
> 107
> 108 /* Search for a valid TLB entry, if one is found, don't remap */
> 109 mmu_write(MMUAR, mmuar);
> 110 mmu_write(MMUOR, MMUOR_STLB | MMUOR_ADR);
> 111 if (mmu_read(MMUSR) & MMUSR_HIT)
> 112 goto end;
> 113
> 114 if (mmuar >= PAGE_OFFSET) {
> 115 mm = &init_mm;
> 116 } else {
> 117 pr_info("load_ksp_mmu: non-kernel mm found: 0x%p\n", task->mm);
> 118 mm = task->mm;
> 119 }
> 120
> 121 if (!mm)
> 122 goto bug;
> 123
> 124 pgd = pgd_offset(mm, mmuar);
> 125 if (pgd_none(*pgd))
> 126 goto bug;
> 127
> 128 p4d = p4d_offset(pgd, mmuar);
> 129 if (p4d_none(*p4d))
> 130 goto bug;
> 131
> 132 pud = pud_offset(p4d, mmuar);
> 133 if (pud_none(*pud))
> 134 goto bug;
> 135
> 136 pmd = pmd_offset(pud, mmuar);
> 137 if (pmd_none(*pmd))
> 138 goto bug;
> 139
> 140 pte = (mmuar >= PAGE_OFFSET) ? pte_offset_kernel(pmd, mmuar)
> 141 : pte_offset_map(pmd, mmuar);
> 142 if (!pte || pte_none(*pte) || !pte_present(*pte))
> 143 goto bug;
> 144
> 145 set_pte(pte, pte_mkyoung(*pte));
> 146 asid = mm->context & 0xff;
> 147 if (!pte_dirty(*pte) && mmuar <= PAGE_OFFSET)
> 148 set_pte(pte, pte_wrprotect(*pte));
> 149
> 150 mmu_write(MMUTR, (mmuar & PAGE_MASK) | (asid << MMUTR_IDN) |
> 151 (((int)(pte->pte) & (int)CF_PAGE_MMUTR_MASK)
> 152 >> CF_PAGE_MMUTR_SHIFT) | MMUTR_V);
> 153
> 154 mmu_write(MMUDR, (pte_val(*pte) & PAGE_MASK) |
> 155 ((pte->pte) & CF_PAGE_MMUDR_MASK) | MMUDR_SZ_8KB | MMUDR_X);
> 156
> 157 mmu_write(MMUOR, MMUOR_ACC | MMUOR_UAA);
> 158
> 159 goto end;
> 160
> 161 bug:
> 162 pr_info("ksp load failed: mm=0x%p ksp=0x08%lx\n", mm, mmuar);
> 163 end:
> > 164 if (pte && mmuar < PAGE_OFFSET)
> 165 pte_unmap(pte);
> 166 local_irq_restore(flags);
> 167 }
> 168
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
I'm sorry, it appears that I've increased the number of smatch warnings on
m68k: but since it was already complaining about "mmuar >= PAGE_OFFSET"s
there, I'm not going to feel very guilty about my "mmuar < PAGE_OFFSET";
and I've no idea of the significance of PAGE_OFFSET 0 on m68k. Over to
you - but I expect ignoring this will continue to be the right answer :)
Thanks,
Hugh