[PATCH 1/2] efi: Add dependency on M-mode for RISC-V

[Sean Anderson]

On 9/28/20 2:24 PM, Heinrich Schuchardt wrote:
> On 28.09.20 19:15, Sean Anderson wrote:
>> On 9/28/20 12:27 PM, Heinrich Schuchardt wrote:
>>> On 28.09.20 18:08, Sean Anderson wrote:
>>>> >From section 2.3.7 of the UEFI specification:
>>>>
>>>>> RISC-V UEFI will only be executed in machine mode. The machine mode has
>>>>> the highest privilege and this mode is the only mandatory privilege level
>>>>> for RISC-V platforms; all other privilege levels are optional depending
>>>>> on the platform requirements. Machine mode is the first mode entered at
>>>>> the power-on reset. This level is used in UEFI for low-level access to a
>>>>> hardware platform.
>>>>
>>>> Signed-off-by: Sean Anderson <seanga2 at gmail.com>
>>>> ---
>>>>
>>>>  lib/efi_loader/Kconfig | 2 ++
>>>>  1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
>>>> index bad1a29ba8..2197c84bf3 100644
>>>> --- a/lib/efi_loader/Kconfig
>>>> +++ b/lib/efi_loader/Kconfig
>>>> @@ -10,6 +10,8 @@ config EFI_LOADER
>>>>  	depends on !EFI_STUB || !X86_64 || EFI_STUB_64BIT
>>>>  	# We need EFI_STUB_32BIT to be set on x86_32 with EFI_STUB
>>>>  	depends on !EFI_STUB || !X86 || X86_64 || EFI_STUB_32BIT
>>>> +	# RISC-V UEFI must run in machine mode
>>>> +	depends on !RISCV || RISCV_M_MODE
>>>>  	default y if !ARM || SYS_CPU = armv7 || SYS_CPU = armv8
>>>>  	select LIB_UUID
>>>>  	select HAVE_BLOCK_DEVICE
>>>>
>>>
>>> Hello Sean,
>>>
>>> the specification is wrong. A change request has been made to correct
>>> the specification. We should not change U-Boot here.
>>>
>>> See the discussion in this thread:
>>> https://lists.linaro.org/pipermail/boot-architecture/2020-September/001481.html
>>>
>>> Best regards
>>>
>>> Heinrich
>>>
>>
>> Thanks for linking that. I'm glad some of these issues are being addressed. However, I am concerned about your suggestion
>>
>>> * Don't trust the values of tp and gp when entered
>>>   from the payloads world.
>>
>> Because tp *must* be trusted in S-Mode...
>>
>> Of course, all this could be averted by adding an sbi_get_mhartid function...
> 
> I thought only the secondary hart uses tp in U-Boot.
> 
> Best regards
> 
> Heinrich
> 

So UEFI is only ever ran on a single hart? I thought one of the
advantages of UEFI was that it could initialize devices in parallel.

--Sean