[PATCH v2 04/13] arm64: decouple early fixmap init from linear mapping

[Ard Biesheuvel]

On 8 January 2016 at 13:00, Catalin Marinas <catalin.marinas at arm.com> wrote:
> On Wed, Dec 30, 2015 at 04:26:03PM +0100, Ard Biesheuvel wrote:
>> @@ -583,33 +555,42 @@ void __init early_fixmap_init(void)
>>       unsigned long addr = FIXADDR_START;
>>
>>       pgd = pgd_offset_k(addr);
>> -     pgd_populate(&init_mm, pgd, bm_pud);
>> -     pud = pud_offset(pgd, addr);
>> -     pud_populate(&init_mm, pud, bm_pmd);
>> -     pmd = pmd_offset(pud, addr);
>> -     pmd_populate_kernel(&init_mm, pmd, bm_pte);
>> +#if CONFIG_PGTABLE_LEVELS > 3
>> +     if (pgd_none(*pgd)) {
>> +             static pud_t bm_pud[PTRS_PER_PUD] __pgdir;
>> +
>> +             pgd_populate(&init_mm, pgd, bm_pud);
>> +             memblock_reserve(__pa(bm_pud), sizeof(bm_pud));
>> +     }
>> +     pud = (pud_t *)__phys_to_kimg(pud_offset_phys(pgd, addr));
>> +#else
>> +     pud = (pud_t *)pgd;
>> +#endif
>> +#if CONFIG_PGTABLE_LEVELS > 2
>> +     if (pud_none(*pud)) {
>> +             static pmd_t bm_pmd[PTRS_PER_PMD] __pgdir;
>> +
>> +             pud_populate(&init_mm, pud, bm_pmd);
>> +             memblock_reserve(__pa(bm_pmd), sizeof(bm_pmd));
>> +     }
>> +     pmd = (pmd_t *)__phys_to_kimg(pmd_offset_phys(pud, addr));
>> +#else
>> +     pmd = (pmd_t *)pud;
>> +#endif
>> +     if (pmd_none(*pmd)) {
>> +             static pte_t bm_pte[PTRS_PER_PTE] __pgdir;
>> +
>> +             pmd_populate_kernel(&init_mm, pmd, bm_pte);
>> +             memblock_reserve(__pa(bm_pte), sizeof(bm_pte));
>> +     }
>> +     __fixmap_pte = (pte_t *)__phys_to_kimg(pmd_page_paddr(*pmd));
>
> I haven't tried but could you not avoid the #if and just rely on the
> pud_none() etc. definitions to be 0 and the compiler+linker optimising
> the irrelevant code out?
>

I tried but it requires some tinkering so I gave up. I can have
another go based on the latest version (which will look a bit
different)