linux-kernel - Re: [RFC PATCH 2/7] riscv: Allow to dynamically define VA

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Date:   Tue, 7 Apr 2020 01:12:31 -0400
From:   Alex Ghiti <alex@...ti.fr>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>, zong.li@...ive.com,
        anup@...infault.org, Christoph Hellwig <hch@....de>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/7] riscv: Allow to dynamically define VA_BITS


On 4/3/20 11:17 AM, Palmer Dabbelt wrote:
> On Sun, 22 Mar 2020 04:00:23 PDT (-0700), alex@...ti.fr wrote:
>> With 4-level page table folding at runtime, we don't know at compile time
>> the size of the virtual address space so we must set VA_BITS dynamically
>> so that sparsemem reserves the right amount of memory for struct pages.
>>
>> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
>> ---
>>  arch/riscv/Kconfig                 | 10 ----------
>>  arch/riscv/include/asm/pgtable.h   | 10 +++++++++-
>>  arch/riscv/include/asm/sparsemem.h |  2 +-
>>  3 files changed, 10 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index f5f3d474504d..8e4b1cbcf2c2 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -99,16 +99,6 @@ config ZONE_DMA32
>>      bool
>>      default y if 64BIT
>>
>> -config VA_BITS
>> -    int
>> -    default 32 if 32BIT
>> -    default 39 if 64BIT
>> -
>> -config PA_BITS
>> -    int
>> -    default 34 if 32BIT
>> -    default 56 if 64BIT
>> -
>>  config PAGE_OFFSET
>>      hex
>>      default 0xC0000000 if 32BIT && MAXPHYSMEM_2GB
>> diff --git a/arch/riscv/include/asm/pgtable.h 
>> b/arch/riscv/include/asm/pgtable.h
>> index 185ffe3723ec..dce401eed1d3 100644
>> --- a/arch/riscv/include/asm/pgtable.h
>> +++ b/arch/riscv/include/asm/pgtable.h
>> @@ -26,6 +26,14 @@
>>  #endif /* CONFIG_64BIT */
>>
>>  #ifdef CONFIG_MMU
>> +#ifdef CONFIG_64BIT
>> +#define VA_BITS        39
>> +#define PA_BITS        56
>> +#else
>> +#define VA_BITS        32
>> +#define PA_BITS        34
> 
> We've moved to 32-bit physical addresses on rv32 in Linux.  The mismatch 
> was
> causing too many issues in generic code.

Ok I missed this one, thanks.

> 
>> +#endif
>> +
>>  /* Number of entries in the page global directory */
>>  #define PTRS_PER_PGD    (PAGE_SIZE / sizeof(pgd_t))
>>  /* Number of entries in the page table */
>> @@ -108,7 +116,7 @@ extern pgd_t swapper_pg_dir[];
>>   * position vmemmap directly below the VMALLOC region.
>>   */
>>  #define VMEMMAP_SHIFT \
>> -    (CONFIG_VA_BITS - PAGE_SHIFT - 1 + STRUCT_PAGE_MAX_SHIFT)
>> +    (VA_BITS - PAGE_SHIFT - 1 + STRUCT_PAGE_MAX_SHIFT)
>>  #define VMEMMAP_SIZE    BIT(VMEMMAP_SHIFT)
>>  #define VMEMMAP_END    (VMALLOC_START - 1)
>>  #define VMEMMAP_START    (VMALLOC_START - VMEMMAP_SIZE)
>> diff --git a/arch/riscv/include/asm/sparsemem.h 
>> b/arch/riscv/include/asm/sparsemem.h
>> index 45a7018a8118..f08d72155bc8 100644
>> --- a/arch/riscv/include/asm/sparsemem.h
>> +++ b/arch/riscv/include/asm/sparsemem.h
>> @@ -4,7 +4,7 @@
>>  #define _ASM_RISCV_SPARSEMEM_H
>>
>>  #ifdef CONFIG_SPARSEMEM
>> -#define MAX_PHYSMEM_BITS    CONFIG_PA_BITS
>> +#define MAX_PHYSMEM_BITS    PA_BITS
>>  #define SECTION_SIZE_BITS    27
>>  #endif /* CONFIG_SPARSEMEM */
> 
> Aside from the 32-bit PA issue:
> 
> Reviewed-by: Palmer Dabbelt <palmerdabbelt@...gle.com>

Thanks,

Alex