On Tue, Sep 19, 2023 at 09:15:19AM +0100, Jean-Philippe Brucker wrote:
> On Mon, Sep 18, 2023 at 05:37:47PM +0100, Robin Murphy wrote:
> > > diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> > > index 17dcd826f5c2..3649586f0e5c 100644
> > > --- a/drivers/iommu/virtio-iommu.c
> > > +++ b/drivers/iommu/virtio-iommu.c
> > > @@ -189,6 +189,12 @@ static int viommu_sync_req(struct viommu_dev *viommu)
> > > int ret;
> > > unsigned long flags;
> > > + /*
> > > + * .iotlb_sync_map and .flush_iotlb_all may be called before the viommu
> > > + * is initialized e.g. via iommu_create_device_direct_mappings()
> > > + */
> > > + if (!viommu)
> > > + return 0;
> >
> > Minor nit: I'd be inclined to make that check explicitly in the places where
> > it definitely is expected, rather than allowing *any* sync to silently do
> > nothing if called incorrectly. Plus then they could use
> > vdomain->nr_endpoints for consistency with the equivalent checks elsewhere
> > (it did take me a moment to figure out how we could get to .iotlb_sync_map
> > with a NULL viommu without viommu_map_pages() blowing up first...)
This makes more sense to me
Ultimately this driver should reach a point where every iommu_domain
always has a non-null domain->viommu because it will be set during
alloc.
But it can still have nr_endpoints == 0, doesn't it make sense to
avoid sync in this case?
(btw this driver is missing locking around vdomain->nr_endpoints)
> They're not strictly equivalent: this check works around a temporary issue
> with the IOMMU core, which calls map/unmap before the domain is
> finalized.
Where? The above points to iommu_create_device_direct_mappings() but
it doesn't because the pgsize_bitmap == 0:
static int iommu_create_device_direct_mappings(struct iommu_domain *domain,
struct device *dev)
{
struct iommu_resv_region *entry;
struct list_head mappings;
unsigned long pg_size;
int ret = 0;
pg_size = domain->pgsize_bitmap ? 1UL << __ffs(domain->pgsize_bitmap) : 0;
INIT_LIST_HEAD(&mappings);
if (WARN_ON_ONCE(iommu_is_dma_domain(domain) && !pg_size))
Indeed, the driver should be failing all map's until the domain is
finalized because it has no way to check the IOVA matches the eventual
aperture.
Jason
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