Fail to boot 5.15 on mpc8347 with either debug_pagealloc or nobats

[Christophe Leroy]

Le 04/12/2021 à 15:10, Maxime Bizon a écrit :
> 
> On Saturday 04 Dec 2021 à 10:01:07 (+0000), Christophe Leroy wrote:
> 
>> In fact BAT4 is wrong. Both virtual and physical address of a 64M BAT
>> must be 64M aligned. I think the display is wrong as well (You took it
> 
> oh so hardware does simple bitmask after all
> 
> I got fooled by the lack of guard in the bat setup code, so I assumed
> magical hardware

I guess all the guard is in the comment ...

/*
  * Set up one of the I/D BAT (block address translation) register pairs.
  * The parameters are not checked; in particular size must be a power
  * of 2 between 128k and 256M.
  */
void __init setbat(int index, unsigned long virt, phys_addr_t phys,
		   unsigned int size, pgprot_t prot)


> 
>> from ptdump ?), BEPI and BRPN must be anded with complement of BL.
> 
> yes that was ptdump code with seq_printf replaced by printk
> 
> ptdump code is correct but iif the bat addresses are correctly
> aligned, maybe add a safeguard like this ?
> 
> index 85062ce2d849..f7c5cf62ef41 100644
> --- a/arch/powerpc/mm/book3s32/mmu.c
> +++ b/arch/powerpc/mm/book3s32/mmu.c
> @@ -275,6 +279,10 @@ void __init setbat(int index, unsigned long virt, phys_addr_t phys,
>                         (unsigned long long)phys);
>                  return;
>          }
> +
> +       WARN_ON(!is_power_of_2(size));
> +       WARN_ON((phys & (size - 1)));
> +       WARN_ON((virt & (size - 1)));
>          bat = BATS[index];
> 

Yes we could add some check allthough I'd go for a 'pr_err()' like when 
no BAT is available.

> 
>> So here your 64M BAT maps 0xf8000000-0xfbffffff, therefore the address
>> 0xfd3fce00 is not mapped by any BAT hence the OOPS.
> 
> ok I think I found the issue:
> 
> diff --git a/arch/powerpc/mm/kasan/book3s_32.c b/arch/powerpc/mm/kasan/book3s_32.c
> index 35b287b0a8da..fcbb9a136c1a 100644
> --- a/arch/powerpc/mm/kasan/book3s_32.c
> +++ b/arch/powerpc/mm/kasan/book3s_32.c
> @@ -12,14 +12,14 @@ int __init kasan_init_region(void *start, size_t size)
>          unsigned long k_end = (unsigned long)kasan_mem_to_shadow(start + size);
>          unsigned long k_cur = k_start;
>          int k_size = k_end - k_start;
> -       int k_size_base = 1 << (ffs(k_size) - 1);
> +       int k_size_base = 1 << (fls(k_size) - 1);
>          int ret;
>          void *block;
>   
>          block = memblock_alloc(k_size, k_size_base);
>   
>          if (block && k_size_base >= SZ_128K && k_start == ALIGN(k_start, k_size_base)) {
> -               int shift = ffs(k_size - k_size_base);
> +               int shift = fls(k_size - k_size_base);
>                  int k_size_more = shift ? 1 << (shift - 1) : 0;
>   
>                  setbat(-1, k_start, __pa(block), k_size_base, PAGE_KERNEL);
> 
> 
> 

Not sure it is that simple.

I'm cooking a patch reusing the block_size() function in mm/book3s32/mmu.c

Christophe