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From:   Song Shuai <suagrfillet@gmail.com>
Date:   Wed, 2 Aug 2023 01:05:23 +0000
Message-ID: <CAAYs2=g2sm=mdoET5tMwBTPwpc-Um-2Xabt9QCaWmAi_VfWTYg@mail.gmail.com>
Subject: Re: [PATCH] riscv: Correct the MODULES_VADDR
To:     Guo Ren <guoren@kernel.org>
Cc:     Alexandre Ghiti <alexghiti@rivosinc.com>, paul.walmsley@sifive.com,
        palmer@dabbelt.com, aou@eecs.berkeley.edu,
        akpm@linux-foundation.org, sergey.matyukevich@syntacore.com,
        david@redhat.com, wangkefeng.wang@huawei.com,
        panqinglin2020@iscas.ac.cn, woodrow.shen@sifive.com,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
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Guo Ren <guoren@kernel.org> =E4=BA=8E2023=E5=B9=B48=E6=9C=881=E6=97=A5=E5=
=91=A8=E4=BA=8C 23:20=E5=86=99=E9=81=93=EF=BC=9A
>
> On Tue, Aug 1, 2023 at 8:05=E2=80=AFAM Alexandre Ghiti <alexghiti@rivosin=
c.com> wrote:
> >
> > Hi Song,
> >
> > On Tue, Aug 1, 2023 at 1:10=E2=80=AFPM Song Shuai <suagrfillet@gmail.co=
m> wrote:
> > >
> > > As Documentation/riscv/vm-layout.rst describes, the 2G-sized "modules=
, BPF"
> > > area should lie right before the "kernel" area. But the current defin=
ition
> > > of MODULES_VADDR isn't consistent with that, so correct it.
> > >
> > > Before this patch, the size of "modules" from print_vm_layout() is no=
t 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@gmail.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/as=
m/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.
>
That's another view to help me understand the definition of
MODULES_VADDR,Thanks.
> --
> Best Regards
>  Guo Ren


--=20
Thanks,
Song