[PATCH 02/12] RISC-V: MAXPHYSMEM_2GB doesn't depend on CMODEL_MEDLOW

[Alexandre ghiti]

Hi Geert,

On 1/11/22 17:04, Geert Uytterhoeven wrote:
> Hi Palmer,
>
> On Fri, Nov 19, 2021 at 5:47 PM Palmer Dabbelt <palmer at rivosinc.com> wrote:
>> From: Palmer Dabbelt <palmer at rivosinc.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 at vger.kernel.org
>> Signed-off-by: Palmer Dabbelt <palmer at rivosinc.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/


>
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -280,7 +280,7 @@ choice
>>                  depends on 32BIT
>>                  bool "1GiB"
>>          config MAXPHYSMEM_2GB
>> -               depends on 64BIT && CMODEL_MEDLOW
>> +               depends on 64BIT
>>                  bool "2GiB"
>>          config MAXPHYSMEM_128GB
>>                  depends on 64BIT && CMODEL_MEDANY
> Gr{oetje,eeting}s,
>
>                          Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-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
>
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