Re: [PATCH] ARM: mmu: fix access to illegal address when using earlycon & memblock=debug

[Rob Herring <robh@kernel.org>]

On Thu, Sep 1, 2022 at 7:54 AM Victor Hassan <victor@allwinnertech.com> wrote:
>
>
>
> On 2022/8/31 20:37, Victor Hassan wrote:
> > On 8/31/2022 7:52 PM, Marek Szyprowski wrote:
> >> Hi Victor,
> >>
> >> On 16.03.2022 03:33, Victor Hassan wrote:
> >>> earlycon uses fixmap to create a memory map,
> >>> So we need to close earlycon before closing fixmap,
> >>> otherwise printk will access illegal addresses.

How? Due to recent changes in how printk and the consoles work or just
because create_mapping() can print? In the latter case, the only
variable input is the phys address. I think most if not all prints
cannot occur.

> >>> After creating a new memory map, we open earlycon again.
> >>>
> >>> Signed-off-by: Victor Hassan <victor@allwinnertech.com>
> >>
> >> This patch landed in linux next-20220831 as commit a76886d117cb ("ARM:
> >> 9223/1: mmu: fix access to illegal address when using earlycon &
> >> memblock=debug"). Unfortunately it breaks booting of all my test boards
> >> which *do not* use earlycon. It can be easily reproduced even with QEMU.
> >>
> >> With kernel compiled from multi_v7_defconfig the following setup boots:
> >>
> >> $ qemu-system-arm -nographic -kernel arch/arm/boot/zImage -append
> >> "console=ttyAMA0 earlycon" -M virt -smp 2 -m 512
> >>
> >> while this one doesn't:
> >>
> >> $ qemu-system-arm -nographic -kernel arch/arm/boot/zImage -append
> >> "console=ttyAMA0" -M virt -smp 2 -m 512
> >>
> >>
> >>> ---
> >>>    arch/arm/mm/mmu.c | 7 +++++++
> >>>    1 file changed, 7 insertions(+)
> >>>
> >>> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> >>> index 274e4f73fd33..f3511f07a7d0 100644
> >>> --- a/arch/arm/mm/mmu.c
> >>> +++ b/arch/arm/mm/mmu.c
> >>> @@ -14,6 +14,7 @@
> >>>    #include <linux/fs.h>
> >>>    #include <linux/vmalloc.h>
> >>>    #include <linux/sizes.h>
> >>> +#include <linux/console.h>
> >>>    #include <asm/cp15.h>
> >>>    #include <asm/cputype.h>
> >>> @@ -1695,6 +1696,9 @@ static void __init early_fixmap_shutdown(void)
> >>>        pmd_clear(fixmap_pmd(va));
> >>>        local_flush_tlb_kernel_page(va);
> >>> +#ifdef CONFIG_FIX_EARLYCON_MEM
> >>> +    console_stop(console_drivers);
> >>> +#endif
> >>>        for (i = 0; i < __end_of_permanent_fixed_addresses; i++) {
> >>>            pte_t *pte;
> >>>            struct map_desc map;
> >>> @@ -1713,6 +1717,9 @@ static void __init early_fixmap_shutdown(void)
> >>>            create_mapping(&map);
> >>>        }
> >>> +#ifdef CONFIG_FIX_EARLYCON_MEM
> >>> +    console_start(console_drivers);
> >>> +#endif
> >>>    }
> >>>    /*
> >>
> >> Best regards
> >
> > Dear Marek,
> > Thank you for the notice. I'll figure it out and feed back to you as
> > soon as possible.
> >
> > Regards,
> > Victor
>
> Hi Marek,
>
> Sorry, didn't take into account that console_drivers is NULL when
> earlycon is not used.
>
> Here is the patch-v2. Please review:
>
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index a49f0b9..a240f38 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -14,6 +14,7 @@
>   #include <linux/fs.h>
>   #include <linux/vmalloc.h>
>   #include <linux/sizes.h>
> +#include <linux/console.h>
>
>   #include <asm/cp15.h>
>   #include <asm/cputype.h>
> @@ -1730,6 +1731,10 @@
>         pmd_clear(fixmap_pmd(va));
>         local_flush_tlb_kernel_page(va);
>
> +#ifdef CONFIG_FIX_EARLYCON_MEM

This is always true for CONFIG_MMU and this file is only built for
CONFIG_MMU. So you don't need it.

> +       if (console_drivers)
> +               console_stop(console_drivers);

console_drivers is a list, so you are only stopping the 1st one.
Couldn't console_lock() be used here?

Also, this should be before pmd_clear().

> +#endif
>         for (i = 0; i < __end_of_permanent_fixed_addresses; i++) {
>                 pte_t *pte;
>                 struct map_desc map;
> @@ -1748,6 +1753,10 @@
>
>                 create_mapping(&map);
>         }
> +#ifdef CONFIG_FIX_EARLYCON_MEM
> +       if (console_drivers)
> +               console_start(console_drivers);
> +#endif
>   }
>
> BTW, should I resend the patch-v2 through the site
> (https://www.armlinux.org.uk/developer/patches/add.php), or should I
> send the patch-v2 through E-mail to Linux-Mainline?
>
> Thanks you.
>
> Regards,
> Victor
>
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