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

[Baolu Lu]

On 2023/6/27 15:54, Tian, Kevin wrote:
> > 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.

Agreed. Does below additional change make sense?

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index e59de7852067..3be88b5f36bb 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -962,6 +962,9 @@ static int 
iommu_create_device_direct_mappings(struct iommu_domain *domain,
        pg_size = domain->pgsize_bitmap ? 1UL << 
__ffs(domain->pgsize_bitmap) : 0;
        INIT_LIST_HEAD(&mappings);

+       if (WARN_ON_ONCE((domain->type & __IOMMU_DOMAIN_PAGING) && 
!pg_size))
+               return -EINVAL;
+
        iommu_get_resv_regions(dev, &mappings);

        /* We need to consider overlapping regions for different devices */
@@ -977,11 +980,6 @@ static int 
iommu_create_device_direct_mappings(struct iommu_domain *domain,
                    !iommu_is_dma_domain(domain))
                        continue;

-               if (WARN_ON_ONCE(!pg_size)) {
-                       ret = -EINVAL;
-                       goto out;
-               }
-
                start = ALIGN(entry->start, pg_size);
                end   = ALIGN(entry->start + entry->length, pg_size);

Best regards,
baolu