[PATCH v10 1/3] riscv: mm: modify pte format for Svnapot

[Qinglin Pan]

Hi Andrew,

On 2022/12/12 15:18, Andrew Jones wrote:
> On Mon, Dec 12, 2022 at 02:55:24PM +0800, panqinglin2020 at iscas.ac.cn wrote:
>> From: Qinglin Pan <panqinglin2020 at iscas.ac.cn>
>>
>> Add one alternative to enable/disable svnapot support, enable this static
>> key when "svnapot" is in the "riscv,isa" field of fdt and SVNAPOT compile
>> option is set. It will influence the behavior of has_svnapot. All code
>> dependent on svnapot should make sure that has_svnapot return true firstly.
>>
>> Modify PTE definition for Svnapot, and creates some functions in pgtable.h
>> to mark a PTE as napot and check if it is a Svnapot PTE. Until now, only
>> 64KB napot size is supported in spec, so some macros has only 64KB version.
>>
>> Signed-off-by: Qinglin Pan <panqinglin2020 at iscas.ac.cn>
>> Reviewed-by: Andrew Jones <ajones at ventanamicro.com>
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 67ef08d33d3a..4b5bb719bc6f 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -397,6 +397,24 @@ config RISCV_ISA_C
>>   
>>   	  If you don't know what to do here, say Y.
>>   
>> +config RISCV_ISA_SVNAPOT
>> +	bool "SVNAPOT extension support"
>> +	depends on 64BIT && MMU
>> +	select RISCV_ALTERNATIVE
> 
> Hmm, shouldn't we also be selecting HUGETLBFS?

RISCV_ISA_SVNAPOT is not dependent on HUGETLBFS, so
it may not be necessary to select HUGETLBFS here? :)

> 
>> +	default y
>> +	help
>> +	  Allow kernel to detect SVNAPOT ISA-extension dynamically in boot time
>                                  ^ the                              ^ s/in/at/
> 
>> +	  and enable its usage.
>> +
>> +	  SVNAPOT extension helps to mark contiguous PTEs as a range
>> +	  of contiguous virtual-to-physical translations, with a naturally
>> +	  aligned power-of-2 (NAPOT) granularity larger than the base 4KB page
>> +	  size. Without CPU's hardware extension, turnning on this feature
>> +	  may cause some little momory leak now.
>> +
>> +	  If you are sure your CPU has not SVNAPOT extension, say N.
>> +	  If you don't know what to do here, say Y.
>> +
> 
> 	The SVNAPOT extension is used to mark contiguous PTEs as a range
> 	of contiguous virtual-to-physical translations for a naturally
> 	aligned power-of-2 (NAPOT) granularity larger than the base 4KB page
> 	size. This option unconditionally allocates some memory for each
> 	NAPOT page size supported by the kernel. When optimizing for low
> 	memory consumption and for platforms without the SVNAPOT extension,
> 	it may be better to say N here.
> 
> 	If you don't know what to do here, say Y.

Your expression is more accurate. I will resend the v10 patchset with
thisparagraph in it. Thanks!

Regards,
Qinglin.

> 
> 
> Thanks,
> drew