On Tue, Sep 19, 2023 at 11:46:49AM -0300, Jason Gunthorpe wrote:
> 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)
Yes, that's on my list
>
> > 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:
__iommu_domain_alloc() sets pgsize_bitmap in this case:
/*
* If not already set, assume all sizes by default; the driver
* may override this later
*/
if (!domain->pgsize_bitmap)
domain->pgsize_bitmap = bus->iommu_ops->pgsize_bitmap;
Thanks,
Jean
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