Failure to boot G4: dt_headr_start=0x01501000

[Mathieu Malaterre]

On Thu, May 23, 2019 at 8:12 PM Christophe Leroy
<christophe.leroy at c-s.fr> wrote:
>
>
>
> On 05/23/2019 10:16 AM, Mathieu Malaterre wrote:
> > On Thu, May 23, 2019 at 11:45 AM Christophe Leroy
> > <christophe.leroy at c-s.fr> wrote:
> >>
> >>
> >>
> >> Le 23/05/2019 à 10:53, Mathieu Malaterre a écrit :
> >>>
> >>> I confirm powerpc/merge does not boot for me (same config). Commit id:
> >>>
> >>> a27eaa62326d (powerpc/merge) Automatic merge of branches 'master',
> >>> 'next' and 'fixes' into merge
> >>
> >> I see in the config you sent me that you have selected CONFIG_KASAN,
> >> which is a big new stuff.
> >>
> >> Can you try without it ?
> >
> > With same config but CONFIG_KASAN=n (on top of a27eaa62326d), I can
> > reproduce the boot failure (no change).
> >
> > Time for bisect ?
> >
>
> I found the issue. In order to be able to support KASAN, the setup of
> segments have moved earlier in the boot. Your problem is a side effect
> of this change.
> Function setup_disp_bat() is supposed to setup BAT3 for btext data.
> But setup_disp_bat() rely on someone setting in disp_BAT the values to
> be loaded into BATs. This is done by btext_prepare_BAT() which is called
> by bootx_init().
> The problem is that bootx_init() is never called, so setup_disp_bat()
> does nothing and the access to btext data is possible because the
> bootloader has set an entry for it in the hash table.
>
> But by setting up the segment earlier, we break the bootloader hash
> table, which shouldn't be an issue if the BATs had been set properly as
> expected.
>
> The problematic commit is 215b823707ce ("powerpc/32s: set up an early
> static hash table for KASAN)"
>
> Here is a dirty fix that works for me when CONFIG_KASAN is NOT set.
> Of course, the real fix has to be to setup the BATs properly, but I
> won't have time to look at that before June. Maybe you can ?
>
> diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
> index 755fab9641d6..fba16970c028 100644
> --- a/arch/powerpc/kernel/head_32.S
> +++ b/arch/powerpc/kernel/head_32.S
> @@ -162,7 +162,6 @@ __after_mmu_off:
>         bl      flush_tlbs
>
>         bl      initial_bats
> -       bl      load_segment_registers
>   #ifdef CONFIG_KASAN
>         bl      early_hash_table
>   #endif
> @@ -920,6 +919,7 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_HPTE_TABLE)
>         RFI
>   /* Load up the kernel context */
>   2:    bl      load_up_mmu
> +       bl      load_segment_registers
>
>   #ifdef CONFIG_BDI_SWITCH
>         /* Add helper information for the Abatron bdiGDB debugger.

With above patch I can boot powerpc/merge just fine. Thanks Christophe !

$ dmesg | head
[    0.000000] printk: bootconsole [udbg0] enabled
[    0.000000] Total memory = 512MB; using 1024kB for hash table
[    0.000000] Linux version 5.1.0+ (malat at debian.org) (gcc version
8.3.0 (Debian 8.3.0-7)) #12 Thu May 23 11:56:33 UTC 2019


> Christophe