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

[Alexey Kardashevskiy]

On 04/16/2015 04:10 PM, David Gibson wrote:
> 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 <aik@xxxxxxxxx>
> > ---
> > 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?


Does this explain?

/*
 * The platform code reserves zero address in iommu_init_table().
 * As we cleared busy bit for page @0 before using bitmap_empty(),
 * we are restoring it now.
 */


> > +	} 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)


--
Alexey
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