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

[Marek Szyprowski <m.szyprowski@samsung.com>]

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.
> 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
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland