On Thu, 23 Nov 2017 15:56:26 +1100 Alexey Kardashevskiy <aik@xxxxxxxxx> wrote: > It is currently possible to have a sparse capability with 1 areas which > starts at 0 and 0 bytes long. One example is: > > Texas Instruments TUSB73x0 SuperSpeed USB 3.0 xHCI Host Controller > [...] > Region 0: Memory at 3fe280000000 (64-bit, non-prefetchable) [size=64K] > Region 2: Memory at 3fe280010000 (64-bit, non-prefetchable) [size=8K] > [...] > Capabilities: [c0] MSI-X: Enable+ Count=8 Masked- > Vector table: BAR=2 offset=00000000 > PBA: BAR=2 offset=00001000 > > With PAGE_SIZE=64K, MSIX BAR occupies the entire BAR2 and cannot be > mapped. > > This makes it explicit - if sparse->areas is empty, then advertise > nr_areas as 0. > > Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx> > --- > > QEMU gets it right as vfio_setup_region_sparse_mmaps() checks for size > after QEMU's 24acf72b9a291ce "vfio: Handle zero-length sparse mmap ranges" > but why not make it explicit in the first place? > > > --- > drivers/vfio/pci/vfio_pci.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c > index f041b1a..a201c45 100644 > --- a/drivers/vfio/pci/vfio_pci.c > +++ b/drivers/vfio/pci/vfio_pci.c > @@ -597,6 +597,10 @@ static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev, > i++; > } > > + /* With all alignments, there are no gaps left to mmap */ > + if (i == 0) > + sparse->nr_areas = 0; > + Ok, but why does 0 become a special case? Shouldn't we set sparse->nr_areas = i? Thanks, Alex > ret = vfio_info_add_capability(caps, VFIO_REGION_INFO_CAP_SPARSE_MMAP, > sparse); > kfree(sparse);
