linux-kernel - Re: [PATCH v2 1/3] arm64: hugetlb: Fix huge_pte_offset to return poisoned page table entries

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Date:   Wed, 7 Jun 2017 14:47:32 +0100
From:   Will Deacon <will.deacon@....com>
To:     Punit Agrawal <punit.agrawal@....com>
Cc:     catalin.marinas@....com, tbaicar@...eaurora.org,
        steve.capper@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, manoj.iyer@...onical.com,
        David Woods <dwoods@...lanox.com>
Subject: Re: [PATCH v2 1/3] arm64: hugetlb: Fix huge_pte_offset to return
 poisoned page table entries

On Wed, May 17, 2017 at 04:23:34PM +0100, Punit Agrawal wrote:
> When memory failure is enabled, a poisoned hugepage pte is marked as a
> swap entry. huge_pte_offset() does not return the poisoned page table
> entries when it encounters PUD/PMD hugepages.
> 
> This behaviour of huge_pte_offset() leads to error such as below when
> munmap is called on poisoned hugepages.
> 
> [  344.165544] mm/pgtable-generic.c:33: bad pmd 000000083af00074.
> 
> Fix huge_pte_offset() to return the poisoned pte which is then
> appropriately handled by the generic layer code.
> 
> Signed-off-by: Punit Agrawal <punit.agrawal@....com>
> Acked-by: Steve Capper <steve.capper@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: David Woods <dwoods@...lanox.com>
> ---
>  arch/arm64/include/asm/pgtable.h |  2 +-
>  arch/arm64/mm/hugetlbpage.c      | 29 ++++++++++-------------------
>  2 files changed, 11 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index c213fdbd056c..6eae342ced6b 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -441,7 +441,7 @@ static inline phys_addr_t pmd_page_paddr(pmd_t pmd)
>  
>  #define pud_none(pud)		(!pud_val(pud))
>  #define pud_bad(pud)		(!(pud_val(pud) & PUD_TABLE_BIT))
> -#define pud_present(pud)	(pud_val(pud))
> +#define pud_present(pud)	pte_present(pud_pte(pud))
>  
>  static inline void set_pud(pud_t *pudp, pud_t pud)
>  {
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index 7514a000e361..69b8200b1cfd 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -136,36 +136,27 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
>  {
>  	pgd_t *pgd;
>  	pud_t *pud;
> -	pmd_t *pmd = NULL;
> -	pte_t *pte = NULL;
> +	pmd_t *pmd;
>  
>  	pgd = pgd_offset(mm, addr);
>  	pr_debug("%s: addr:0x%lx pgd:%p\n", __func__, addr, pgd);
>  	if (!pgd_present(*pgd))
>  		return NULL;
> +
>  	pud = pud_offset(pgd, addr);
> -	if (!pud_present(*pud))
> +	if (pud_none(*pud))
>  		return NULL;

Do you actually need this special case?

> -
> -	if (pud_huge(*pud))
> +	/* swap or huge page */
> +	if (!pud_present(*pud) || pud_huge(*pud))

... couldn't you just add a '|| pud_none(*pud)' in here?

>  		return (pte_t *)pud;
> +	/* table; check the next level */
> +
>  	pmd = pmd_offset(pud, addr);
> -	if (!pmd_present(*pmd))
> +	if (pmd_none(*pmd))
>  		return NULL;
> -
> -	if (pte_cont(pmd_pte(*pmd))) {
> -		pmd = pmd_offset(
> -			pud, (addr & CONT_PMD_MASK));
> -		return (pte_t *)pmd;
> -	}
> -	if (pmd_huge(*pmd))
> +	if (!pmd_present(*pmd) || pmd_huge(*pmd))

Similarly here.

Will