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

[Alexey Kardashevskiy]

On 17/10/2018 12:00, David Gibson wrote:
> On Mon, Oct 15, 2018 at 08:24:15PM +1100, Alexey Kardashevskiy wrote:
>> 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 <aik at ozlabs.ru>
> 
> 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


> 
>> ---
>>  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;
>>  		}
>>  
> 

-- 
Alexey