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

[Alexey Kardashevskiy]

On 04/20/2015 12:46 PM, David Gibson wrote:
> On Fri, Apr 17, 2015 at 08:16:13PM +1000, Alexey Kardashevskiy wrote:
> > 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.
> >   */
>
> Only partly.  What's it reserved for, and why do you know it was
> always set on entry?


Because it is only handled in this file and I can see it in the code. Or I 
did not understand the question here...




--
Alexey
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