Subject: Re: [PATCH kernel v8 15/31] powerpc/iommu: Fix IOMMU ownership control functions

From: David Gibson <[email-masked]>
Date: Thu, 16 Apr 2015 16:10:49 +1000

On Fri, Apr 10, 2015 at 04:30:57PM +1000, Alexey Kardashevskiy wrote:
> This adds missing locks in iommu_take_ownership()/
> iommu_release_ownership().
> 
> This marks all pages busy in iommu_table::it_map in order to catch
> errors if there is an attempt to use this table while ownership over it
> is taken.
> 
> This only clears TCE content if there is no page marked busy in it_map.
> Clearing must be done outside of the table locks as iommu_clear_tce()
> called from iommu_clear_tces_and_put_pages() does this.
> 
> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
> ---
> Changes:
> v5:
> * do not store bit#0 value, it has to be set for zero-based table
> anyway
> * removed test_and_clear_bit
> ---
>  arch/powerpc/kernel/iommu.c | 26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> index 7d6089b..068fe4ff 100644
> --- a/arch/powerpc/kernel/iommu.c
> +++ b/arch/powerpc/kernel/iommu.c
> @@ -1052,17 +1052,28 @@ EXPORT_SYMBOL_GPL(iommu_tce_build);
>  
>  static int iommu_table_take_ownership(struct iommu_table *tbl)
>  {
> -	unsigned long sz = (tbl->it_size + 7) >> 3;
> +	unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
> +	int ret = 0;
> +
> +	spin_lock_irqsave(&tbl->large_pool.lock, flags);
> +	for (i = 0; i < tbl->nr_pools; i++)
> +		spin_lock(&tbl->pools[i].lock);
>  
>  	if (tbl->it_offset == 0)
>  		clear_bit(0, tbl->it_map);
>  
>  	if (!bitmap_empty(tbl->it_map, tbl->it_size)) {
>  		pr_err("iommu_tce: it_map is not empty");
> -		return -EBUSY;
> +		ret = -EBUSY;
> +		if (tbl->it_offset == 0)
> +			set_bit(0, tbl->it_map);

This really needs a comment.  Why on earth are you changing the it_map
on a failure case?

> +	} else {
> +		memset(tbl->it_map, 0xff, sz);
>  	}
>  
> -	memset(tbl->it_map, 0xff, sz);
> +	for (i = 0; i < tbl->nr_pools; i++)
> +		spin_unlock(&tbl->pools[i].lock);
> +	spin_unlock_irqrestore(&tbl->large_pool.lock, flags);
>  
>  	return 0;
>  }
> @@ -1095,7 +1106,11 @@ EXPORT_SYMBOL_GPL(iommu_take_ownership);
>  
>  static void iommu_table_release_ownership(struct iommu_table *tbl)
>  {
> -	unsigned long sz = (tbl->it_size + 7) >> 3;
> +	unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
> +
> +	spin_lock_irqsave(&tbl->large_pool.lock, flags);
> +	for (i = 0; i < tbl->nr_pools; i++)
> +		spin_lock(&tbl->pools[i].lock);
>  
>  	memset(tbl->it_map, 0, sz);
>  
> @@ -1103,6 +1118,9 @@ static void iommu_table_release_ownership(struct iommu_table *tbl)
>  	if (tbl->it_offset == 0)
>  		set_bit(0, tbl->it_map);
>  
> +	for (i = 0; i < tbl->nr_pools; i++)
> +		spin_unlock(&tbl->pools[i].lock);
> +	spin_unlock_irqrestore(&tbl->large_pool.lock, flags);
>  }
>  
>  extern void iommu_release_ownership(struct iommu_table_group *table_group)

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson