[PATCH v2 1/1] efi_loader: architecture specific UEFI setup

[Ard Biesheuvel]

On Wed, 5 Feb 2020 at 05:53, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> RISC-V booting currently is based on a per boot stage lottery to determine
> the active CPU. The Hart State Management (HSM) SBI extension replaces
> this lottery by using a dedicated primary CPU.
>
> Cf. Hart State Management Extension, Extension ID: 0x48534D (HSM)
> https://github.com/riscv/riscv-sbi-doc/blob/master/riscv-sbi.adoc
>
> In this scenario the id of the active hart has to be passed from boot stage
> to boot stage. Using a UEFI variable would provide an easy implementation.
>
> This patch provides a weak function that is called at the end of the setup
> of U-Boot's UEFI sub-system. By overriding this function architecture
> specific UEFI variables or configuration tables can be created.
>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
> Reviewed-by: Atish Patra <atish.patra at wdc.com>

OK, so I have a couple of questions:

- does RISC-V use device tree? if so, why are you not passing the
active hart via a property in the /chosen node? I'd assume the EFI
stub would not care at all about this information, and it would give
you a Linux/RISC-V specific way to convey this information that is
independent of EFI.
- using variables to pass information from firmware to OS only is
overkill, and config tables are preferred, given that they only
require access to the system table. If required, a RISC-V specific
data structure containing boot parameters could be installed as a
configuration table, and the address passed to the startup code in the
kernel proper [rather than just a hart id], allowing you to put any
piece of information you like in there.

Config tables work fine with kexec, btw. It is up to the first OS to
memblock_reserve() the table to guarantee that it is still there at
kexec time, but this applies equally to all other data structures
passed as config tables. Alternatively, in this case, you can
stipulate that it is passed as AcpiReclaim [ignore the 'Acpi' in the
name] which is intended for firmware tables (and we never reclaim it
in linux)

I'd also recommend that RISC-V adopt the same principle as ARM does
when it comes to EFI: call SetVirtualAddressMap in the stub, so that
the kernel proper always sees the same handover state, regardless of
kexec. Additionally, you shouldn't ever modify the EFI memory map
provided by the firmware, so that the kexec kernel sees the exact same
version.




> ---
> v2:
>         reference the Hart State Management Extension in the commit message
> ---
>  include/efi_loader.h       |  3 +++
>  lib/efi_loader/efi_setup.c | 16 ++++++++++++++++
>  2 files changed, 19 insertions(+)
>
> diff --git a/include/efi_loader.h b/include/efi_loader.h
> index d4c59b54c4..d87de85e83 100644
> --- a/include/efi_loader.h
> +++ b/include/efi_loader.h
> @@ -116,6 +116,9 @@ extern efi_uintn_t efi_memory_map_key;
>  extern struct efi_runtime_services efi_runtime_services;
>  extern struct efi_system_table systab;
>
> +/* Architecture specific initialization of the UEFI system */
> +efi_status_t efi_setup_arch_specific(void);
> +
>  extern struct efi_simple_text_output_protocol efi_con_out;
>  extern struct efi_simple_text_input_protocol efi_con_in;
>  extern struct efi_console_control_protocol efi_console_control;
> diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c
> index de7b616c6d..8469f0f43c 100644
> --- a/lib/efi_loader/efi_setup.c
> +++ b/lib/efi_loader/efi_setup.c
> @@ -22,6 +22,17 @@ void __weak allow_unaligned(void)
>  {
>  }
>
> +/**
> + * efi_setup_arch_specific() - architecture specific UEFI setup
> + *
> + * This routine can be used to define architecture specific variables
> + * or configuration tables, e.g. HART id for RISC-V
> + */
> +efi_status_t __weak efi_setup_arch_specific(void)
> +{
> +       return EFI_SUCCESS;
> +}
> +
>  /**
>   * efi_init_platform_lang() - define supported languages
>   *
> @@ -179,6 +190,11 @@ efi_status_t efi_init_obj_list(void)
>         if (ret != EFI_SUCCESS)
>                 goto out;
>
> +       /* Architecture specific setup */
> +       ret = efi_setup_arch_specific();
> +       if (ret != EFI_SUCCESS)
> +               goto out;
> +
>  out:
>         efi_obj_list_initialized = ret;
>         return ret;
> --
> 2.24.1
>