linux-kernel - Re: [RFC PATCH 1/7] riscv: Get rid of compile time logic with MAX_EARLY_MAPPING

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Date:   Tue, 7 Apr 2020 01:12:15 -0400
From:   Alex Ghiti <alex@...ti.fr>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     anup@...infault.org, linux-kernel@...r.kernel.org,
        zong.li@...ive.com, Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org, Christoph Hellwig <hch@....de>
Subject: Re: [RFC PATCH 1/7] riscv: Get rid of compile time logic with
 MAX_EARLY_MAPPING_SIZE



On 4/3/20 11:17 AM, Palmer Dabbelt wrote:
> On Sun, 22 Mar 2020 04:00:22 PDT (-0700), alex@...ti.fr wrote:
>> There is no need to compare at compile time MAX_EARLY_MAPPING_SIZE value
>> with PGDIR_SIZE since MAX_EARLY_MAPPING_SIZE is set to 128MB which is 
>> less
>> than PGDIR_SIZE that is equal to 1GB: that allows to simplify early_pmd
>> definition.
>>
>> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
>> ---
>>  arch/riscv/mm/init.c | 16 ++++------------
>>  1 file changed, 4 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>> index 238bd0033c3f..18bbb426848e 100644
>> --- a/arch/riscv/mm/init.c
>> +++ b/arch/riscv/mm/init.c
>> @@ -247,13 +247,7 @@ static void __init create_pte_mapping(pte_t *ptep,
>>
>>  pmd_t trampoline_pmd[PTRS_PER_PMD] __page_aligned_bss;
>>  pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
>> -
>> -#if MAX_EARLY_MAPPING_SIZE < PGDIR_SIZE
>> -#define NUM_EARLY_PMDS        1UL
>> -#else
>> -#define NUM_EARLY_PMDS        (1UL + MAX_EARLY_MAPPING_SIZE / 
>> PGDIR_SIZE)
>> -#endif
>> -pmd_t early_pmd[PTRS_PER_PMD * NUM_EARLY_PMDS] __initdata 
>> __aligned(PAGE_SIZE);
>> +pmd_t early_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
>>
>>  static pmd_t *__init get_pmd_virt(phys_addr_t pa)
>>  {
>> @@ -267,14 +261,12 @@ static pmd_t *__init get_pmd_virt(phys_addr_t pa)
>>
>>  static phys_addr_t __init alloc_pmd(uintptr_t va)
>>  {
>> -    uintptr_t pmd_num;
>> -
>>      if (mmu_enabled)
>>          return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>>
>> -    pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
>> -    BUG_ON(pmd_num >= NUM_EARLY_PMDS);
>> -    return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
>> +    BUG_ON((va - PAGE_OFFSET) >> PGDIR_SHIFT);
>> +
>> +    return (uintptr_t)early_pmd;
>>  }
>>
>>  static void __init create_pmd_mapping(pmd_t *pmdp,
> 
> My specific worry here was that allyesconfig kernels are quite large, 
> and that
> dropping the code to handle large kernels would make it even harder to boot
> them.  That said, I can't actually get one to boot so I'm happy to just 
> push
> that off until later and drop the code we can't practically use.
> 
> Reviewed-by: Palmer Dabbelt <palmerdabbelt@...gle.com>
> 
> Thanks!
> 

Thanks,

Alex