Re: [PATCH v3 4/5] xen: Add files needed for minimal riscv build

[Bob Eshleman <bobbyeshleman@gmail.com>]

On 5/14/21 11:53 AM, Connor Davis wrote:
> Add arch-specific makefiles and configs needed to build for
> riscv64. Also add a minimal head.S that is a simple infinite loop.
> head.o can be built with
> 
> $ make XEN_TARGET_ARCH=riscv64 SUBSYSTEMS=xen -C xen TARGET=head.o
> 

I recently realized that the Linux kernel build uses `ARCH=riscv`
with 32 vs 64 being differentiated by Kconfig opts (and __riscv_xlen).
I think `riscv64` was inherited by `arm64`.  This is something I'd
like to eventually change the Xen build to (i.e.,
`XEN_TARGET_ARCH=riscv make`) would it be possible for us to get that
in this series?

...

> diff --git a/xen/include/asm-riscv/config.h b/xen/include/asm-riscv/config.h
> new file mode 100644
> index 0000000000..84cb436dc1
> --- /dev/null
> +++ b/xen/include/asm-riscv/config.h
> @@ -0,0 +1,110 @@
> +/******************************************************************************
> + * config.h
> + *
> + * A Linux-style configuration list.
> + */
> +
> +#ifndef __RISCV_CONFIG_H__
> +#define __RISCV_CONFIG_H__
> +

...

> +
> +#ifdef CONFIG_RISCV_64
> +
> +/*
> + * RISC-V Layout:
> + *   0x0000000000000000 - 0x0000003fffffffff (256GB, L2 slots [0-255])
> + *     Unmapped
> + *   0x0000004000000000 - 0xffffffbfffffffff
> + *     Inaccessible: sv39 only supports 39-bit sign-extended VAs.
> + *   0xffffffc000000000 - 0xffffffc0001fffff (2MB, L2 slot [256])
> + *     Unmapped
> + *   0xffffffc000200000 - 0xffffffc0003fffff (2MB, L2 slot [256])
> + *     Xen text, data, bss
> + *   0xffffffc000400000 - 0xffffffc0005fffff (2MB, L2 slot [256])
> + *     Fixmap: special-purpose 4K mapping slots
> + *   0xffffffc000600000 - 0xffffffc0009fffff (4MB, L2 slot [256])
> + *     Early boot mapping of FDT
> + *   0xffffffc000a00000 - 0xffffffc000bfffff (2MB, L2 slot [256])
> + *     Early relocation address, used when relocating Xen and later
> + *     for livepatch vmap (if compiled in)
> + *   0xffffffc040000000 - 0xffffffc07fffffff (1GB, L2 slot [257])
> + *     VMAP: ioremap and early_ioremap
> + *   0xffffffc080000000 - 0xffffffc13fffffff (3GB, L2 slots [258..260])
> + *     Unmapped
> + *   0xffffffc140000000 - 0xffffffc1bfffffff (2GB, L2 slots [261..262])
> + *     Frametable: 48 bytes per page for 133GB of RAM
> + *   0xffffffc1c0000000 - 0xffffffe1bfffffff (128GB, L2 slots [263..390])
> + *     1:1 direct mapping of RAM
> + *   0xffffffe1c0000000 - 0xffffffffffffffff (121GB, L2 slots [391..511])
> + *     Unmapped
> + */
> +
What is the benefit of moving the layout up to 0xffffffc000000000?

-- 
Bobby Eshleman
SE at Vates SAS