Re: [PATCH v3 1/7] mm: Add functions to track page directory modifications

[Catalin Marinas]

Hi Joerg,

On Fri, May 15, 2020 at 04:00:17PM +0200, Joerg Roedel wrote:
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5a323422d783..022fe682af9e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2078,13 +2078,54 @@ static inline pud_t *pud_alloc(struct mm_struct *mm, p4d_t *p4d,
>  	return (unlikely(p4d_none(*p4d)) && __pud_alloc(mm, p4d, address)) ?
>  		NULL : pud_offset(p4d, address);
>  }
> +
> +static inline p4d_t *p4d_alloc_track(struct mm_struct *mm, pgd_t *pgd,
> +				     unsigned long address,
> +				     pgtbl_mod_mask *mod_mask)
> +
> +{
> +	if (unlikely(pgd_none(*pgd))) {
> +		if (__p4d_alloc(mm, pgd, address))
> +			return NULL;
> +		*mod_mask |= PGTBL_PGD_MODIFIED;
> +	}
> +
> +	return p4d_offset(pgd, address);
> +}
> +
>  #endif /* !__ARCH_HAS_5LEVEL_HACK */
>  
> +static inline pud_t *pud_alloc_track(struct mm_struct *mm, p4d_t *p4d,
> +				     unsigned long address,
> +				     pgtbl_mod_mask *mod_mask)
> +{
> +	if (unlikely(p4d_none(*p4d))) {
> +		if (__pud_alloc(mm, p4d, address))
> +			return NULL;
> +		*mod_mask |= PGTBL_P4D_MODIFIED;
> +	}
> +
> +	return pud_offset(p4d, address);
> +}

This patch causes a kernel panic on arm64 (and possibly powerpc, I
haven't tried). arm64 still uses the 5level-fixup.h and pud_alloc()
checks for the empty p4d with pgd_none() instead of p4d_none().

The patch below fixes it:

-----------------------8<-----------------------------------