On Wed, Sep 23, 2015 at 09:07:06PM +1000, David Gibson wrote:
> On Wed, Sep 23, 2015 at 12:10:46PM +0200, Thomas Huth wrote:
> > On 17/09/15 15:09, David Gibson wrote:
> > > The current vfio core code assumes that the host IOMMU is capable of
> > > mapping any IOVA the guest wants to use to where we need. However, real
> > > IOMMUs generally only support translating a certain range of IOVAs (the
> > > "DMA window") not a full 64-bit address space.
> > >
> > > The common x86 IOMMUs support a wide enough range that guests are very
> > > unlikely to go beyond it in practice, however the IOMMU used on IBM Power
> > > machines - in the default configuration - supports only a much more
> > > limited
> > > IOVA range, usually 0..2GiB.
> > >
> > > If the guest attempts to set up an IOVA range that the host IOMMU can't
> > > map, qemu won't report an error until it actually attempts to map a bad
> > > IOVA. If guest RAM is being mapped directly into the IOMMU (i.e. no guest
> > > visible IOMMU) then this will show up very quickly. If there is a guest
> > > visible IOMMU, however, the problem might not show up until much later
> > > when
> > > the guest actually attempt to DMA with an IOVA the host can't handle.
> > >
> > > This patch adds a test so that we will detect earlier if the guest is
> > > attempting to use IOVA ranges that the host IOMMU won't be able to deal
> > > with.
> > >
> > > For now, we assume that "Type1" (x86) IOMMUs can support any IOVA, this is
> > > incorrect, but no worse than what we have already. We can't do better for
> > > now because the Type1 kernel interface doesn't tell us what IOVA range the
> > > IOMMU actually supports.
> > >
> > > For the Power "sPAPR TCE" IOMMU, however, we can retrieve the supported
> > > IOVA range and validate guest IOVA ranges against it, and this patch does
> > > so.
> > >
> > > Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
> > > ---
> > > hw/vfio/common.c | 42
> > > +++++++++++++++++++++++++++++++++++++++---
> > > include/hw/vfio/vfio-common.h | 6 ++++++
> > > 2 files changed, 45 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > > index 9953b9c..c37f1a1 100644
> > > --- a/hw/vfio/common.c
> > > +++ b/hw/vfio/common.c
> > > @@ -344,14 +344,23 @@ static void vfio_listener_region_add(MemoryListener
> > > *listener,
> > > if (int128_ge(int128_make64(iova), llend)) {
> > > return;
> > > }
> > > + end = int128_get64(llend);
> > > +
> > > + if ((iova < container->iommu_data.min_iova)
> > > + || ((end - 1) > container->iommu_data.max_iova)) {
> >
> > (Too much paranthesis for my taste ;-))
>
> Yes, well, we've already established our tastes differ on that point.
>
> > > + error_report("vfio: IOMMU container %p can't map guest IOVA
> > > region"
> > > + " 0x%"HWADDR_PRIx"..0x%"HWADDR_PRIx,
> > > + container, iova, end - 1);
> > > + ret = -EFAULT; /* FIXME: better choice here? */
> >
> > Maybe -EINVAL? ... but -EFAULT also sounds ok for me.
>
> I try to avoid EINVAL unless it's clearly the only right choice. So
> many things use it that it tends to be very unhelpful when you get one.
>
> > > + goto fail;
> > > + }
> > ...
> > > @@ -712,6 +732,22 @@ static int vfio_connect_container(VFIOGroup *group,
> > > AddressSpace *as)
> > > ret = -errno;
> > > goto free_container_exit;
> > > }
> > > +
> > > + /*
> > > + * FIXME: This only considers the host IOMMU' 32-bit window.
> > > + * At some point we need to add support for the optional
> > > + * 64-bit window and dynamic windows
> > > + */
> > > + info.argsz = sizeof(info);
> > > + ret = ioctl(fd, VFIO_IOMMU_SPAPR_TCE_GET_INFO, &info);
> > > + if (ret) {
> > > + error_report("vfio: VFIO_IOMMU_SPAPR_TCE_GET_INFO failed:
> > > %m");
> >
> > Isn't that %m a glibc extension only? ... Well, this code likely only
> > runs on Linux with a glibc, so it likely doesn't matter, I guess...
>
> Yes, it is, but it's already used extensively within qemu.
>
> > > + ret = -errno;
> > > + goto free_container_exit;
> > > + }
> > > + container->iommu_data.min_iova = info.dma32_window_start;
> > > + container->iommu_data.max_iova = container->iommu_data.min_iova
> > > + + info.dma32_window_size - 1;
> > > } else {
> > > error_report("vfio: No available IOMMU models");
> > > ret = -EINVAL;
> > > diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> > > index aff18cd..88ec213 100644
> > > --- a/include/hw/vfio/vfio-common.h
> > > +++ b/include/hw/vfio/vfio-common.h
> > > @@ -71,6 +71,12 @@ typedef struct VFIOContainer {
> > > MemoryListener listener;
> > > int error;
> > > bool initialized;
> > > + /*
> > > + * FIXME: This assumes the host IOMMU can support only a
> > > + * single contiguous IOVA window. We may need to generalize
> > > + * that in future
> > > + */
> > > + hwaddr min_iova, max_iova;
> >
> > Should that maybe be dma_addr_t instead of hwaddr ?
>
> Ah, yes it probably should.
Actually, on further consideration, no it shouldn't. hwaddr is what's
used throughout the VFIO code, in address_space_translate() and in
IOMMUTLBEntry, for both sides of the translation. In fact, I'm not
entirely convinced there's any reason to have dma_addr_t distinct from
hwaddr at all, but that's a cleanup for some other day.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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