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

["Baicar, Tyler" <tbaicar@codeaurora.org>]

On 4/12/2017 8:04 AM, 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@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Steve Capper <steve.capper@arm.com>
> Cc: David Woods <dwoods@mellanox.com>
Tested-by: Tyler Baicar <tbaicar@codeaurora.org>

Thanks,
Tyler
> ---
>   arch/arm64/mm/hugetlbpage.c | 20 +++++++++++++++-----
>   1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index 7514a000e361..5f1832165d69 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -143,15 +143,24 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long 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))
> -		return NULL;
>   
> -	if (pud_huge(*pud))
> +	pud = pud_offset(pgd, addr);
> +	/*
> +	 * In case of HW Poisoning, a hugepage pud/pmd can contain
> +	 * poisoned entries. Poisoned entries are marked as swap
> +	 * entries.
> +	 *
> +	 * For puds/pmds that are not present, check to see if it
> +	 * could be a swap entry (!present and !none).
> +	 */
> +	if ((!pte_present(pud_pte(*pud)) && !pud_none(*pud)) || pud_huge(*pud))
>   		return (pte_t *)pud;
> +
>   	pmd = pmd_offset(pud, addr);
> -	if (!pmd_present(*pmd))
> +	if (pmd_none(*pmd))
>   		return NULL;
> +	if (!pmd_present(*pmd) && !pmd_none(*pmd))
> +		return (pte_t *)pmd;
>   
>   	if (pte_cont(pmd_pte(*pmd))) {
>   		pmd = pmd_offset(
> @@ -160,6 +169,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
>   	}
>   	if (pmd_huge(*pmd))
>   		return (pte_t *)pmd;
> +
>   	pte = pte_offset_kernel(pmd, addr);
>   	if (pte_present(*pte) && pte_cont(*pte)) {
>   		pte = pte_offset_kernel(

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