Re: [Qemu-devel] [RFC PATCH 03/10] vfio: Check guest IOVA ranges against host IOMMU capabilities

[Thomas Huth <thuth@redhat.com>]

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 <david@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 ;-))

> +        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.

> +        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...

> +            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 ?

>      } iommu_data;
>      QLIST_HEAD(, VFIOGuestIOMMU) giommu_list;
>      QLIST_HEAD(, VFIOGroup) group_list;
> 

 Thomas