Re: [PATCH v2] mm: Fix modifying of page protection by insert_pfn_pmd()

[Jan Kara <jack@suse.cz>]

On Tue 02-04-19 17:21:25, Aneesh Kumar K.V wrote:
> With some architectures like ppc64, set_pmd_at() cannot cope with
> a situation where there is already some (different) valid entry present.
> 
> Use pmdp_set_access_flags() instead to modify the pfn which is built to
> deal with modifying existing PMD entries.
> 
> This is similar to
> commit cae85cb8add3 ("mm/memory.c: fix modifying of page protection by insert_pfn()")
> 
> We also do similar update w.r.t insert_pfn_pud eventhough ppc64 don't support
> pud pfn entries now.
> 
> Without this patch we also see the below message in kernel log
> "BUG: non-zero pgtables_bytes on freeing mm:"
> 
> CC: stable@vger.kernel.org
> Reported-by: Chandan Rajendra <chandan@linux.ibm.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
> Changes from v1:
> * Fix the pgtable leak 
> 
>  mm/huge_memory.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 404acdcd0455..165ea46bf149 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -755,6 +755,21 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
>  	spinlock_t *ptl;
>  
>  	ptl = pmd_lock(mm, pmd);
> +	if (!pmd_none(*pmd)) {
> +		if (write) {
> +			if (pmd_pfn(*pmd) != pfn_t_to_pfn(pfn)) {
> +				WARN_ON_ONCE(!is_huge_zero_pmd(*pmd));
> +				goto out_unlock;
> +			}
> +			entry = pmd_mkyoung(*pmd);
> +			entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> +			if (pmdp_set_access_flags(vma, addr, pmd, entry, 1))
> +				update_mmu_cache_pmd(vma, addr, pmd);
> +		}
> +
> +		goto out_unlock;
> +	}
> +
>  	entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
>  	if (pfn_t_devmap(pfn))
>  		entry = pmd_mkdevmap(entry);
> @@ -766,11 +781,16 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
>  	if (pgtable) {
>  		pgtable_trans_huge_deposit(mm, pmd, pgtable);
>  		mm_inc_nr_ptes(mm);
> +		pgtable = NULL;
>  	}
>  
>  	set_pmd_at(mm, addr, pmd, entry);
>  	update_mmu_cache_pmd(vma, addr, pmd);
> +
> +out_unlock:
>  	spin_unlock(ptl);
> +	if (pgtable)
> +		pte_free(mm, pgtable);
>  }
>  
>  vm_fault_t vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> @@ -821,6 +841,20 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
>  	spinlock_t *ptl;
>  
>  	ptl = pud_lock(mm, pud);
> +	if (!pud_none(*pud)) {
> +		if (write) {
> +			if (pud_pfn(*pud) != pfn_t_to_pfn(pfn)) {
> +				WARN_ON_ONCE(!is_huge_zero_pud(*pud));
> +				goto out_unlock;
> +			}
> +			entry = pud_mkyoung(*pud);
> +			entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
> +			if (pudp_set_access_flags(vma, addr, pud, entry, 1))
> +				update_mmu_cache_pud(vma, addr, pud);
> +		}
> +		goto out_unlock;
> +	}
> +
>  	entry = pud_mkhuge(pfn_t_pud(pfn, prot));
>  	if (pfn_t_devmap(pfn))
>  		entry = pud_mkdevmap(entry);
> @@ -830,6 +864,8 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
>  	}
>  	set_pud_at(mm, addr, pud, entry);
>  	update_mmu_cache_pud(vma, addr, pud);
> +
> +out_unlock:
>  	spin_unlock(ptl);
>  }
>  
> -- 
> 2.20.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR