Re: [RFC PATCH 2/7] riscv: Allow to dynamically define VA_BITS

[Alex Ghiti]

On 4/3/20 11:17 AM, Palmer Dabbelt wrote:
> On Sun, 22 Mar 2020 04:00:23 PDT (-0700), alex@xxxxxxxx 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@xxxxxxxx>
> > ---
> > Âarch/riscv/KconfigÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ | 10 ----------
> > Âarch/riscv/include/asm/pgtable.hÂÂ | 10 +++++++++-
> > Âarch/riscv/include/asm/sparsemem.h |Â 2 +-
> > Â3 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
> > ÂÂÂÂ bool
> > ÂÂÂÂ default y if 64BIT
> >
> > -config VA_BITS
> > -ÂÂÂ int
> > -ÂÂÂ default 32 if 32BIT
> > -ÂÂÂ default 39 if 64BIT
> > -
> > -config PA_BITS
> > -ÂÂÂ int
> > -ÂÂÂ default 34 if 32BIT
> > -ÂÂÂ default 56 if 64BIT
> > -
> > Âconfig PAGE_OFFSET
> > ÂÂÂÂ hex
> > ÂÂÂÂ 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 @@
> > Â#endif /* CONFIG_64BIT */
> >
> > Â#ifdef CONFIG_MMU
> > +#ifdef CONFIG_64BIT
> > +#define VA_BITSÂÂÂÂÂÂÂ 39
> > +#define PA_BITSÂÂÂÂÂÂÂ 56
> > +#else
> > +#define VA_BITSÂÂÂÂÂÂÂ 32
> > +#define PA_BITSÂÂÂÂÂÂÂ 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
> > +
> > Â/* Number of entries in the page global directory */
> > Â#define PTRS_PER_PGDÂÂÂ (PAGE_SIZE / sizeof(pgd_t))
> > Â/* Number of entries in the page table */
> > @@ -108,7 +116,7 @@ extern pgd_t swapper_pg_dir[];
> > Â * position vmemmap directly below the VMALLOC region.
> > Â */
> > Â#define VMEMMAP_SHIFT \
> > -ÂÂÂ (CONFIG_VA_BITS - PAGE_SHIFT - 1 + STRUCT_PAGE_MAX_SHIFT)
> > +ÂÂÂ (VA_BITS - PAGE_SHIFT - 1 + STRUCT_PAGE_MAX_SHIFT)
> > Â#define VMEMMAP_SIZEÂÂÂ BIT(VMEMMAP_SHIFT)
> > Â#define VMEMMAP_ENDÂÂÂ (VMALLOC_START - 1)
> > Â#define VMEMMAP_STARTÂÂÂ (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 @@
> > Â#define _ASM_RISCV_SPARSEMEM_H
> >
> > Â#ifdef CONFIG_SPARSEMEM
> > -#define MAX_PHYSMEM_BITSÂÂÂ CONFIG_PA_BITS
> > +#define MAX_PHYSMEM_BITSÂÂÂ PA_BITS
> > Â#define SECTION_SIZE_BITSÂÂÂ 27
> > Â#endif /* CONFIG_SPARSEMEM */
>
> Aside from the 32-bit PA issue:
>
> Reviewed-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>

Thanks,

Alex