Re: [PATCH] riscv: kbuild: add virtual memory system selection

[Bin Meng <bmeng.cn@gmail.com>]

On Sat, Jul 27, 2019 at 4:00 AM Paul Walmsley <paul.walmsley@sifive.com> wrote:
>
>
> The RISC-V specifications currently define three virtual memory
> translation systems: Sv32, Sv39, and Sv48.  Sv32 is currently specific
> to 32-bit systems; Sv39 and Sv48 are currently specific to 64-bit
> systems.  The current kernel only supports Sv32 and Sv39, but we'd
> like to start preparing for Sv48.  As an initial step, allow the
> virtual memory translation system to be selected via kbuild, and stop
> the build if an option is selected that the kernel doen't currently
> support.
>
> This patch currently has no functional impact.
>
> Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
> Cc: Alexandre Ghiti <alex@ghiti.fr>
> ---
>  arch/riscv/Kconfig                  | 43 +++++++++++++++++++++++++++++
>  arch/riscv/include/asm/pgtable-32.h |  4 +++
>  arch/riscv/include/asm/pgtable-64.h |  4 +++
>  3 files changed, 51 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 59a4727ecd6c..8ef64fe2c2b3 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -155,6 +155,49 @@ config MODULE_SECTIONS
>         bool
>         select HAVE_MOD_ARCH_SPECIFIC
>
> +choice
> +       prompt "Virtual Memory System"
> +       default RISCV_VM_SV32 if 32BIT
> +       default RISCV_VM_SV39 if 64BIT
> +       help
> +         The RISC-V Instruction Set Manual Volume II: Privileged
> +         Architecture defines several different "virtual memory
> +         systems" which specify virtual and physical address formats
> +         and the structure of page table entries.  This determines
> +         the amount of virtual address space present and how it is
> +         translated into physical addresses.
> +
> +       config RISCV_VM_SV32
> +               depends on 32BIT
> +               bool "RISC-V Sv32"
> +               help
> +                 The Sv32 virtual memory system is a page-based
> +                 address and page table format for RV32 systems.
> +                 It specifies a translation between 32-bit virtual
> +                 addresses and 33-bit physical addresses, via a
> +                 two-stage page table layout.
> +       config RISCV_VM_SV39
> +               depends on 64BIT
> +               bool "RISC-V Sv39"
> +               help
> +                 The Sv39 virtual memory system is a page-based
> +                 address and page table format for RV64 systems.
> +                 It specifies a translation between 39-bit virtual
> +                 addresses and 40-bit physical addresses, via a

The spec does not mention 40-bit physical addresses, but 56-bit.

> +                 three-stage page table layout.
> +       config RISCV_VM_SV48
> +               depends on 64BIT
> +               bool "RISC-V Sv48"
> +               help
> +                 The Sv48 virtual memory system is a page-based
> +                 address and page table format for RV64 systems.
> +                 It specifies a translation between 48-bit virtual
> +                 addresses and 49-bit physical addresses, via a

ditto.

> +                 four-stage page table layout.
> +
> +endchoice
> +
> +
>  choice
>         prompt "Maximum Physical Memory"
>         default MAXPHYSMEM_2GB if 32BIT
> diff --git a/arch/riscv/include/asm/pgtable-32.h b/arch/riscv/include/asm/pgtable-32.h
> index b0ab66e5fdb1..86d41a04735b 100644
> --- a/arch/riscv/include/asm/pgtable-32.h
> +++ b/arch/riscv/include/asm/pgtable-32.h
> @@ -6,6 +6,10 @@
>  #ifndef _ASM_RISCV_PGTABLE_32_H
>  #define _ASM_RISCV_PGTABLE_32_H
>
> +#if !defined(CONFIG_RISCV_VM_SV32)
> +#error Only Sv32 supported
> +#endif
> +
>  #include <asm-generic/pgtable-nopmd.h>
>  #include <linux/const.h>
>
> diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
> index 74630989006d..86935595115d 100644
> --- a/arch/riscv/include/asm/pgtable-64.h
> +++ b/arch/riscv/include/asm/pgtable-64.h
> @@ -6,6 +6,10 @@
>  #ifndef _ASM_RISCV_PGTABLE_64_H
>  #define _ASM_RISCV_PGTABLE_64_H
>
> +#if !defined(CONFIG_RISCV_VM_SV39)
> +#error Only Sv39 supported for now
> +#endif
> +
>  #include <linux/const.h>
>
>  #define PGDIR_SHIFT     30
> --

Regards,
Bin