Re: [PATCH v5 02/11] powerpc/kernel/iommu: Add new iommu_table_in_use() helper

On 20/07/2021 15:38, Leonardo Brás wrote:

Hello Fred, thanks for this feedback!

Sorry if I miss anything, this snippet was written for v1 over an year
ago, and I have not taken a look at it ever since.

On Mon, 2021-07-19 at 15:53 +0200, Frederic Barrat wrote:

quoted

On 16/07/2021 10:27, Leonardo Bras wrote:

quoted

@@ -1099,18 +1105,13 @@ int iommu_take_ownership(struct iommu_table

*tbl)
         for (i = 0; i < tbl->nr_pools; i++)
                 spin_lock_nest_lock(&tbl->pools[i].lock, &tbl-

quoted

large_pool.lock);

   
-       iommu_table_release_pages(tbl);
-
-       if (!bitmap_empty(tbl->it_map, tbl->it_size)) {
+       if (iommu_table_in_use(tbl)) {
                 pr_err("iommu_tce: it_map is not empty");
                 ret = -EBUSY;
-               /* Undo iommu_table_release_pages, i.e. restore
bit#0, etc */
-               iommu_table_reserve_pages(tbl, tbl-

quoted

it_reserved_start,

-                               tbl->it_reserved_end);
-       } else {
-               memset(tbl->it_map, 0xff, sz);
         }
   
+       memset(tbl->it_map, 0xff, sz);
+

So if the table is not empty, we fail (EBUSY) but we now also
completely
overwrite the bitmap. It was in an unexpected state, but we're making
it
worse. Or am I missing something?

IIRC there was a reason to do that at the time, but TBH I don't really
remember it, and by looking at the code right now you seem to be
correct about this causing trouble.

I will send a v6 fixing it soon.
Please review the remaining patches for some issue I may be missing.

Alexey, any comments on that?

Agree with Fred, this is a bug, EBUSY is not that unexpected :-/ Thanks,

quoted

    Fred

Again, thank you for reviewing Fred!
Best regards,
Leonardo Bras

-- 
Alexey