linux-kernel - Re: [PATCH] riscv: Correct the MODULES

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Date:   Tue, 1 Aug 2023 19:20:14 -0400
From:   Guo Ren <guoren@...nel.org>
To:     Alexandre Ghiti <alexghiti@...osinc.com>
Cc:     Song Shuai <suagrfillet@...il.com>, paul.walmsley@...ive.com,
        palmer@...belt.com, aou@...s.berkeley.edu,
        akpm@...ux-foundation.org, sergey.matyukevich@...tacore.com,
        david@...hat.com, wangkefeng.wang@...wei.com,
        panqinglin2020@...as.ac.cn, woodrow.shen@...ive.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: Correct the MODULES_VADDR

On Tue, Aug 1, 2023 at 8:05 AM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
>
> Hi Song,
>
> On Tue, Aug 1, 2023 at 1:10 PM Song Shuai <suagrfillet@...il.com> wrote:
> >
> > As Documentation/riscv/vm-layout.rst describes, the 2G-sized "modules, BPF"
> > area should lie right before the "kernel" area. But the current definition
> > of MODULES_VADDR isn't consistent with that, so correct it.
> >
> > Before this patch, the size of "modules" from print_vm_layout() is not 2G.
> >
> > [    0.000000]      modules : 0xffffffff2ff2f000 - 0xffffffffae600000 (2022 MB)
> > [    0.000000]       lowmem : 0xff60000000000000 - 0xff60000040000000 (1024 MB)
> > [    0.000000]       kernel : 0xffffffffae600000 - 0xffffffffffffffff (1305 MB)
> >
> > After this patch, the size is 2G.
> >
> > [    0.000000]      modules : 0xffffffff3a000000 - 0xffffffffba000000 (2048 MB)
> > [    0.000000]       lowmem : 0xff60000000000000 - 0xff60000040000000 (1024 MB)
> > [    0.000000]       kernel : 0xffffffffba000000 - 0xffffffffffffffff (1119 MB)
> >
> > Signed-off-by: Song Shuai <suagrfillet@...il.com>
> > ---
> >  arch/riscv/include/asm/pgtable.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > index 75970ee2bda2..7c57e17fc758 100644
> > --- a/arch/riscv/include/asm/pgtable.h
> > +++ b/arch/riscv/include/asm/pgtable.h
> > @@ -53,8 +53,8 @@
> >  #ifdef CONFIG_64BIT
> >  /* This is used to define the end of the KASAN shadow region */
> >  #define MODULES_LOWEST_VADDR   (KERNEL_LINK_ADDR - SZ_2G)
> > -#define MODULES_VADDR          (PFN_ALIGN((unsigned long)&_end) - SZ_2G)
> >  #define MODULES_END            (PFN_ALIGN((unsigned long)&_start))
> > +#define MODULES_VADDR          (MODULES_END - SZ_2G)
> >  #endif
> >
> >  /*
> > --
> > 2.20.1
> >
>
> The documentation is approximative, the modules must stay within a 2GB
> window to *all* the kernel symbols, hence the __end - 2G, not __start.
Thus, the ftrace detour trampoline could cover all kernel symbols.

-- 
Best Regards
 Guo Ren