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SubjectRe: [PATCH kernel v8 15/31] powerpc/iommu: Fix IOMMU ownership control functions
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@ozlabs.ru>
> >>---
> >>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?

--
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
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