linux-kernel - Re: [PATCH] riscv: mm: Update the comment of CONFIG_PAGE

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Date:   Sun, 29 Oct 2023 21:53:10 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Song Shuai <songshuaishuai@...ylab.org>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, ajones@...tanamicro.com,
        alexghiti@...osinc.com, anup@...infault.org, samuel@...lland.org,
        rppt@...nel.org, suagrfillet@...il.com, panqinglin2020@...as.ac.cn,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: mm: Update the comment of CONFIG_PAGE_OFFSET

On Thu, Sep 14, 2023 at 2:52 PM Song Shuai <songshuaishuai@...ylab.org> wrote:
>
>
>
> 在 2023/9/14 12:59, Guo Ren 写道:
> > On Wed, Aug 9, 2023 at 11:11 AM Song Shuai <songshuaishuai@...ylab.org> wrote:
> >>
> >> From: Song Shuai <suagrfillet@...il.com>
> >>
> >> 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@...il.com>
> >> ---
> >>   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.

I mean:

#define PAGE_OFFSET_L5         _AC(0xff60000000000000, UL)
#define PAGE_OFFSET_L4         _AC(0xffffaf8000000000, UL)
#define PAGE_OFFSET_L3         _AC(0xffffffd800000000, UL)
#define PAGE_OFFSET_L2         _AC(0xC0000000)

#ifdef CONFIG_MMU
#ifdef CONFIG_64BIT
#define PAGE_OFFSET             kernel_map.page_offset
#else /* CONFIG_64BIT */
#define PAGE_OFFSET             PAGE_OFFSET_L2
#endif /* CONFIG_64BIT */
#else /* CONFIG_MMU */
#define PAGE_OFFSET             0x80000000
#endif /* CONFIG_MMU */

kernel_map.page_offset = _AC(PAGE_OFFSET_L5, UL);

The kernel_map.page_offset is no use to CONFIG_32BIT.

Remove the CONFIG_PAGE_OFFSET, and put all PAGE_OFFSET* together to
ease maintenance and reading.



>
> 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
>


-- 
Best Regards
 Guo Ren