Re: [PATCH 1/1] soft_dirty: fix soft_dirty during THP split

[Pavel Emelyanov <xemul@virtuozzo.com>]

On 08/19/2016 03:41 PM, Andrea Arcangeli wrote:
> Transfer the soft_dirty from pmd to pte during THP splits.
> 
> This fix avoids losing the soft_dirty bit and avoids userland memory
> corruption in the checkpoint.

Nasty :( Thanks for catching this!

> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>

Acked-by: Pavel Emelyanov <xemul@virtuozzo.com>

> ---
>  mm/huge_memory.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index b9570b5..cb95a83 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1512,7 +1512,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>  	struct page *page;
>  	pgtable_t pgtable;
>  	pmd_t _pmd;
> -	bool young, write, dirty;
> +	bool young, write, dirty, soft_dirty;
>  	unsigned long addr;
>  	int i;
>  
> @@ -1546,6 +1546,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>  	write = pmd_write(*pmd);
>  	young = pmd_young(*pmd);
>  	dirty = pmd_dirty(*pmd);
> +	soft_dirty = pmd_soft_dirty(*pmd);
>  
>  	pmdp_huge_split_prepare(vma, haddr, pmd);
>  	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
> @@ -1562,6 +1563,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>  			swp_entry_t swp_entry;
>  			swp_entry = make_migration_entry(page + i, write);
>  			entry = swp_entry_to_pte(swp_entry);
> +			if (soft_dirty)
> +				entry = pte_swp_mksoft_dirty(entry);
>  		} else {
>  			entry = mk_pte(page + i, vma->vm_page_prot);
>  			entry = maybe_mkwrite(entry, vma);
> @@ -1569,6 +1572,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>  				entry = pte_wrprotect(entry);
>  			if (!young)
>  				entry = pte_mkold(entry);
> +			if (soft_dirty)
> +				entry = pte_mksoft_dirty(entry);
>  		}
>  		if (dirty)
>  			SetPageDirty(page + i);
> .
> 

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