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

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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@xxxxxxxxxxxx> wrote:
From: Palmer Dabbelt <palmer@xxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx
Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
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@xxxxxxxxxxxxx/



--- 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@xxxxxxxxxxxxxx

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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