[PATCH v3] riscv: Allow to downgrade paging mode from the command

[Alexandre Ghiti]

Hi Conor,

On 1/23/23 12:53, Conor Dooley wrote:
> Hey Alex,
>
> On Mon, Jan 23, 2023 at 11:48:41AM +0100, Alexandre Ghiti wrote:
>> Add 2 early command line parameters that allow to downgrade satp mode
>> (using the same naming as x86):
>> - "no5lvl": use a 4-level page table (down from sv57 to sv48)
>> - "no4lvl": use a 3-level page table (down from sv57/sv48 to sv39)
>>
>> Note that going through the device tree to get the kernel command line
>> works with ACPI too since the efi stub creates a device tree anyway with
>> the command line.
>>
>> Also, as those params are treated very early in the boot process and we
>> use standard device tree functions that may be kasan instrumented, we
>> only enable them for !KASAN configurations.
>>
>> Reviewed-by: Björn Töpel <bjorn at kernel.org>
>> Signed-off-by: Alexandre Ghiti <alexghiti at rivosinc.com>
>> ---
> A changelog would be nice here, especially since this is a resend.


I think you may have commented the wrong patch, this one is wrong, hence 
the resend!


>
>>   .../admin-guide/kernel-parameters.txt         |  9 ++-
>>   arch/riscv/mm/init.c                          | 72 +++++++++++++++++--
>>   2 files changed, 74 insertions(+), 7 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 6cfa6e3996cf..fd647412ec91 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -3578,8 +3578,15 @@
>>   			emulation library even if a 387 maths coprocessor
>>   			is present.
>>   
>> -	no5lvl		[X86-64] Disable 5-level paging mode. Forces
>> +	no4lvl		[RISCV] Disable 4-level and 5-level paging modes. Forces
>> +			kernel to use 3-level paging instead.
>> +			Note: On RISC-V, this can't be used when KASAN is
>> +			enabled.
>> +
>> +	no5lvl		[X86-64,RISCV] Disable 5-level paging mode. Forces
>>   			kernel to use 4-level paging instead.
>> +			Note: On RISC-V, this can't be used when KASAN is
>> +			enabled.
>>   
>>   	nofsgsbase	[X86] Disables FSGSBASE instructions.
>>   
> For the improved descriptions & commit message:
> Reviewed-by: Conor Dooley <conor.dooley at microchip.com>


Thanks for that, would you mind adding that to the resend patch?

Thanks again,

Alex


>
> Thanks,
> Conor.
>
>
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