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

From: David Gibson <[email-masked]>
Date: Wed, 17 Oct 2018 12:00:22 +1100

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 <[email-masked]>

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?

> ---
>  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