On Tue, Feb 4, 2020 at 11:43 PM Ard Biesheuvel ard.biesheuvel@linaro.org wrote:
On Wed, 5 Feb 2020 at 05:53, Heinrich Schuchardt xypron.glpk@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@gmx.de Reviewed-by: Atish Patra atish.patra@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?
Yes. RISC-V uses device tree. Technically, we can pass the active hart by a DT property but that means we have to modify the DT in OpenSBI (RISC-V specific run time service provider). We have been trying to avoid that if possible so that DT is not bounced around. This also limits U-Boot to have its own device tree.
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.
Yes. EFI stub doesn't care about this information. However, it needs to save the information somewhere so that it can pass to the real kernel after exiting boot time services.
- 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.
Sounds good to me. I will experiment with configuration table and send the EFI stub patch series.
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.
Sure. There is no kexec implementation available now. We will keep this in mind while implementing it. Thanks!
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