Re: [PATCH kernel 3/4] powerpc/mm/iommu: Make mm_iommu_new() fail on existing regions

On Wed, Oct 17, 2018 at 02:34:32PM +1100, Alexey Kardashevskiy wrote:

On 17/10/2018 12:00, David Gibson wrote:

quoted

On Mon, Oct 15, 2018 at 08:24:15PM +1100, Alexey Kardashevskiy wrote:

quoted

Since we are going to have 2 different preregistering helpers, let's
make it clear that mm_iommu_new() is only for the normal (i.e. not device)
memory and for existing areas mm_iommu_get() should be used instead.

Signed-off-by: Alexey Kardashevskiy <redacted>

I think the idea is sensible.  However (and, yes, this is really an
existing bug) - shouldn't we check for a request to add anything
overlapping with an existing region, not just one that exactly
matches?

The overlap check is below the changed hunk:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/mm/mmu_context_iommu.c#n150

Ah, right.

In that case can't you just drop this whole if.  I don't see that
there's any use in giving different error codes for "tried to register
exactly a region you registered before" and "tried to register a
region overlapping one you registered before.

quoted

quoted

---
 arch/powerpc/mm/mmu_context_iommu.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
index a8c4a3c..839dbce 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c

@@ -141,8 +141,7 @@ long mm_iommu_new(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 	list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list,
 			next) {
 		if ((mem->ua == ua) && (mem->entries == entries)) {
-			++mem->used;
-			*pmem = mem;
+			ret = -EBUSY;
 			goto unlock_exit;
 		}
 

-- 
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