Re: [PATCH] riscv: mm: Update the comment of CONFIG_PAGE_OFFSET

[Song Shuai]

在 2023/9/14 12:59, Guo Ren 写道:
> On Wed, Aug 9, 2023 at 11:11 AM Song Shuai <songshuaishuai@xxxxxxxxxxx> wrote:
> > From: Song Shuai <suagrfillet@xxxxxxxxx>
> >
> > Since the commit 011f09d12052 set sv57 as default for CONFIG_64BIT,
> > the comment of CONFIG_PAGE_OFFSET should be updated too.
> >
> > Fixes: 011f09d12052 ("riscv: mm: Set sv57 on defaultly")
> > Signed-off-by: Song Shuai <suagrfillet@xxxxxxxxx>
> > ---
> >   arch/riscv/include/asm/page.h | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> > index b55ba20903ec..53c00164c042 100644
> > --- a/arch/riscv/include/asm/page.h
> > +++ b/arch/riscv/include/asm/page.h
> > @@ -33,8 +33,8 @@
> >   #define PAGE_OFFSET            _AC(CONFIG_PAGE_OFFSET, UL)
> Why not remove CONFIG_PAGE_OFFSET and define PAGE_OFFSET_L2 ?
CONFIG_PAGE_OFFSET holds the first memory address regarding the 
different CONFIGs (MMU,32BIT,64BIT).

As for 64BIT, it actually represents "PAGE_OFFSET_L5" for Sv57 page mode 
defaultly. And the real page mode may be downgraded from kernel cmdline 
or restricted by the hardware, so the PAGE_OFFSET_L3/L4 was defined to 
set the real PAGE_OFFSET.

IIUC, the "PAGE_OFFSET_L2" you specified might be the "PAGE_OFFSET_L5" I 
previously mentioned,
If not, the PAGE_OFFSET_L2 semantically means the page offset for 
32BIT's default Sv32 page mode,and it has already been held in 
CONFIG_PAGE_OFFSET too.

So IMO there is no need to touch CONFIG_PAGE_OFFSET in this context.

Please correct me If I'm wrong.
> >   #endif
> >   /*
> > - * By default, CONFIG_PAGE_OFFSET value corresponds to SV48 address space so
> > - * define the PAGE_OFFSET value for SV39.
> > + * By default, CONFIG_PAGE_OFFSET value corresponds to SV57 address space so
> > + * define the PAGE_OFFSET value for SV48 and SV39.
> >    */
> >   #define PAGE_OFFSET_L4         _AC(0xffffaf8000000000, UL)
> >   #define PAGE_OFFSET_L3         _AC(0xffffffd800000000, UL)
> > --
> > 2.20.1

--
Thanks
Song Shuai