linux-kernel - Re: [PATCH] riscv: errata: andes: Probe IOCP during boot stage

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Message-ID: <CAMuHMdXozB7PVOZM+SQa9D6Zca3x_+LE63RhmBGPDvmOma1fUA@mail.gmail.com>
Date:   Wed, 22 Nov 2023 09:23:44 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Prabhakar <prabhakar.csengg@...il.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Yu Chien Peter Lin <peterlin@...estech.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH] riscv: errata: andes: Probe IOCP during boot stage

Hi Prabhakar,

On Tue, Nov 21, 2023 at 9:25 PM Prabhakar <prabhakar.csengg@...il.com> wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
>
> We should be probing for IOCP during boot stage only. As we were probing
> for IOCP for all the stages this caused the below issue during module-init
> stage,
>
> [9.019104] Unable to handle kernel paging request at virtual address ffffffff8100d3a0
> [9.027153] Oops [#1]
> [9.029421] Modules linked in: rcar_canfd renesas_usbhs i2c_riic can_dev spi_rspi i2c_core
> [9.037686] CPU: 0 PID: 90 Comm: udevd Not tainted 6.7.0-rc1+ #57
> [9.043756] Hardware name: Renesas SMARC EVK based on r9a07g043f01 (DT)
> [9.050339] epc : riscv_noncoherent_supported+0x10/0x3e
> [9.055558]  ra : andes_errata_patch_func+0x4a/0x52
> [9.060418] epc : ffffffff8000d8c2 ra : ffffffff8000d95c sp : ffffffc8003abb00
> [9.067607]  gp : ffffffff814e25a0 tp : ffffffd80361e540 t0 : 0000000000000000
> [9.074795]  t1 : 000000000900031e t2 : 0000000000000001 s0 : ffffffc8003abb20
> [9.081984]  s1 : ffffffff015b57c7 a0 : 0000000000000000 a1 : 0000000000000001
> [9.089172]  a2 : 0000000000000000 a3 : 0000000000000000 a4 : ffffffff8100d8be
> [9.096360]  a5 : 0000000000000001 a6 : 0000000000000001 a7 : 000000000900031e
> [9.103548]  s2 : ffffffff015b57d7 s3 : 0000000000000001 s4 : 000000000000031e
> [9.110736]  s5 : 8000000000008a45 s6 : 0000000000000500 s7 : 000000000000003f
> [9.117924]  s8 : ffffffc8003abd48 s9 : ffffffff015b1140 s10: ffffffff8151a1b0
> [9.125113]  s11: ffffffff015b1000 t3 : 0000000000000001 t4 : fefefefefefefeff
> [9.132301]  t5 : ffffffff015b57c7 t6 : ffffffd8b63a6000
> [9.137587] status: 0000000200000120 badaddr: ffffffff8100d3a0 cause: 000000000000000f
> [9.145468] [<ffffffff8000d8c2>] riscv_noncoherent_supported+0x10/0x3e
> [9.151972] [<ffffffff800027e8>] _apply_alternatives+0x84/0x86
> [9.157784] [<ffffffff800029be>] apply_module_alternatives+0x10/0x1a
> [9.164113] [<ffffffff80008fcc>] module_finalize+0x5e/0x7a
> [9.169583] [<ffffffff80085cd6>] load_module+0xfd8/0x179c
> [9.174965] [<ffffffff80086630>] init_module_from_file+0x76/0xaa
> [9.180948] [<ffffffff800867f6>] __riscv_sys_finit_module+0x176/0x2a8
> [9.187365] [<ffffffff80889862>] do_trap_ecall_u+0xbe/0x130
> [9.192922] [<ffffffff808920bc>] ret_from_exception+0x0/0x64
> [9.198573] Code: 0009 b7e9 6797 014d a783 85a7 c799 4785 0717 0100 (0123) aef7
> [9.205994] ---[ end trace 0000000000000000 ]---
>
> This is because we called riscv_noncoherent_supported() for all the stages
> during IOCP probe. riscv_noncoherent_supported() function sets
> noncoherent_supported variable to true which has an annotation set to
> "__ro_after_init" due to which we were seeing the above splat. Fix this by
> probing IOCP during boot stage only.
>
> Fixes: e021ae7f5145 ("riscv: errata: Add Andes alternative ports")
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>

Thanks for your patch!

> --- a/arch/riscv/errata/andes/errata.c
> +++ b/arch/riscv/errata/andes/errata.c
> @@ -60,7 +60,8 @@ void __init_or_module andes_errata_patch_func(struct alt_entry *begin, struct al
>                                               unsigned long archid, unsigned long impid,
>                                               unsigned int stage)
>  {
> -       errata_probe_iocp(stage, archid, impid);
> +       if (stage == RISCV_ALTERNATIVES_BOOT)
> +               errata_probe_iocp(stage, archid, impid);
>
>         /* we have nothing to patch here ATM so just return back */
>  }

I believe this still causes errata_probe_iocp() to be called twice:
once from apply_boot_alternatives(), and a second time (if CONFIG_MMU=y)
from apply_vdso_alternatives().  Is that OK?

Perhaps instead you want to add a check to errata_probe_iocp() (after
the check for CONFIG_ERRATA_ANDES_CMO), to bail out if the function
was called before?

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