linux-kernel - Re: [PATCH 02/12] RISC-V: MAXPHYSMEM_2GB doesn't depend on CMODEL

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Date:   Fri, 14 Jan 2022 11:12:28 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Alexandre ghiti <alex@...ti.fr>
Cc:     Palmer Dabbelt <palmer@...osinc.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup.patel@....com>,
        heinrich.schuchardt@...onical.com,
        Atish Patra <atish.patra@....com>,
        Bin Meng <bin.meng@...driver.com>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Damien Le Moal <damien.lemoal@....com>,
        Jens Axboe <axboe@...nel.dk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH 02/12] RISC-V: MAXPHYSMEM_2GB doesn't depend on CMODEL_MEDLOW

Hi Alex,

On Tue, Jan 11, 2022 at 5:14 PM Alexandre ghiti <alex@...ti.fr> wrote:
> On 1/11/22 17:04, Geert Uytterhoeven wrote:
> > On Fri, Nov 19, 2021 at 5:47 PM Palmer Dabbelt <palmer@...osinc.com> wrote:
> >> From: Palmer Dabbelt <palmer@...osinc.com>
> >>
> >> For non-relocatable kernels we need to be able to link the kernel at
> >> approximately PAGE_OFFSET, thus requiring medany (as medlow requires the
> >> code to be linked within 2GiB of 0).  The inverse doesn't apply, though:
> >> since medany code can be linked anywhere it's fine to link it close to
> >> 0, so we can support the smaller memory config.
> >>
> >> Fixes: de5f4b8f634b ("RISC-V: Define MAXPHYSMEM_1GB only for RV32")
> >> Cc: stable@...r.kernel.org
> >> Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
> > Thanks for your patch, which is now commit 9f36b96bc70f9707 ("RISC-V:
> > MAXPHYSMEM_2GB doesn't depend on CMODEL_MEDLOW").
> >
> >> I found this when going through the savedefconfig diffs for the K210
> >> defconfigs.  I'm not entirely sure they're doing the right thing here
> >> (they should probably be setting CMODEL_LOW to take advantage of the
> >> better code generation), but I don't have any way to test those
> >> platforms so I don't want to change too much.
> > I can confirm MAXPHYSMEM_2GB works on K210 with CMODEL_MEDANY.
> >
> > As the Icicle has 1760 MiB of RAM, I gave it a try with MAXPHYSMEM_2GB
> > (and CMODEL_MEDANY), too.  Unfortunately it crashes very early
> > (needs earlycon to see):
> >
> >      OF: fdt: Ignoring memory range 0x80000000 - 0x80200000
> >      Machine model: Microchip PolarFire-SoC Icicle Kit
> >      printk: debug: ignoring loglevel setting.
> >      earlycon: ns16550a0 at MMIO32 0x0000000020100000 (options '115200n8')
> >      printk: bootconsole [ns16550a0] enabled
> >      printk: debug: skip boot console de-registration.
> >      efi: UEFI not found.
> >      Unable to handle kernel paging request at virtual address ffffffff87e00001
> >      Oops [#1]
> >      Modules linked in:
> >      CPU: 0 PID: 0 Comm: swapper Not tainted 5.16.0-08771-g85515233477d #56
> >      Hardware name: Microchip PolarFire-SoC Icicle Kit (DT)
> >      epc : fdt_check_header+0x14/0x208
> >       ra : early_init_dt_verify+0x16/0x94
> >      epc : ffffffff802ddacc ra : ffffffff8082415a sp : ffffffff81203ee0
> >       gp : ffffffff812ec3a8 tp : ffffffff8120cd80 t0 : 0000000000000005
> >       t1 : 0000001040000000 t2 : ffffffff80000000 s0 : ffffffff81203f00
> >       s1 : ffffffff87e00000 a0 : ffffffff87e00000 a1 : 000000040ffffce7
> >       a2 : 00000000000000e7 a3 : ffffffff8080394c a4 : 0000000000000000
> >       a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000000000000
> >       s2 : ffffffff81203f98 s3 : 8000000a00006800 s4 : fffffffffffffff3
> >       s5 : 0000000000000000 s6 : 0000000000000001 s7 : 0000000000000000
> >       s8 : 0000000020236c20 s9 : 0000000000000000 s10: 0000000000000000
> >       s11: 0000000000000000 t3 : 0000000000000018 t4 : 00ff000000000000
> >       t5 : 0000000000000000 t6 : 0000000000000010
> >      status: 0000000200000100 badaddr: ffffffff87e00001 cause: 000000000000000d
> >      [<ffffffff802ddacc>] fdt_check_header+0x14/0x208
> >      [<ffffffff8082415a>] early_init_dt_verify+0x16/0x94
> >      [<ffffffff80802dee>] setup_arch+0xec/0x4ec
> >      [<ffffffff80800700>] start_kernel+0x88/0x6d6
> >      random: get_random_bytes called from
> > print_oops_end_marker+0x22/0x44 with crng_init=0
> >      ---[ end trace 903df1a0ade0b876 ]---
> >      Kernel panic - not syncing: Attempted to kill the idle task!
> >      ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
> >
> > So the FDT is at 0xffffffff87e00000, i.e. at 0x7e00000 from the start
> > of virtual memory (CONFIG_PAGE_OFFSET=0xffffffff80000000), and thus
> > within the 2 GiB range.
>
>
> I think you have just encountered what I suspected and mentioned in [1]:
> we recently moved the kernel to the PAGE_OFFSET address used with
> MAXPHYSMEM_2GB.
>
> I would try to cherry-pick [1] and see if that works better :)
>
> Alex
>
> [1]
> https://patchwork.kernel.org/project/linux-riscv/patch/20211206104657.433304-6-alexandre.ghiti@canonical.com/

Thanks, works fine with just that patch (needed small changes), or with
the full series.

Tested-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds