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

[Victor Hassan]

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.
> > After creating a new memory map, we open earlycon again.
> >
> > Signed-off-by: Victor Hassan <victor@xxxxxxxxxxxxxxxxx>
>
> 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