RE: [PATCH 1/2] iommu: Prevent RESV_DIRECT devices from blocking domains

[Tian, Kevin]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Tuesday, June 13, 2023 11:15 AM
> 
> On 6/12/23 4:28 PM, Liu, Jingqi wrote:
> > On 6/7/2023 11:51 AM, Lu Baolu wrote:
> >> -
> >> -    BUG_ON(!domain->pgsize_bitmap);
> >> -
> >> -    pg_size = 1UL << __ffs(domain->pgsize_bitmap);
> >> +    pg_size = domain->pgsize_bitmap ? 1UL <<
> >> __ffs(domain->pgsize_bitmap) : 0;
> > Would it be better to add the following check here?
> >      if (WARN_ON(!pg_size))
> >              return -EINVAL;
> >
> > Instead of checking latter in the loop as follows.
> >      if (WARN_ON_ONCE(!pg_size)) {
> >              ret = -EINVAL;
> >              goto out;
> >      }
> 
> I am afraid no. Only the paging domains need a valid pg_size. That's the
> reason why I put it after the iommu_is_dma_domain() check. The previous
> code has the same behavior too.
> 

You could also add the dma domain check here. pg_size is static
then it makes more sense to verify it once instead of in a loop.