Re: [Qemu-devel] [PATCH qemu] vfio/spapr: Allow fallback to SPAPR TCE IOMMU v1

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 22 Nov 2017 16:15:52 +1100
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> The vfio_iommu_spapr_tce driver always advertises v1 and v2 IOMMU support,
> however PR KVM (a special version of KVM designed to work in
> a paravirtualized system; these days used for nested virtualizaion) only
> supports the "pseries" platform which does not support v2. Since there is
> no way to choose the IOMMU version in QEMU, it fails to start.

Seems like the bug is then in advertising v2 support when it doesn't
exist.  Isn't that a kernel bug?  Otherwise I think this is a long
standing bug, since QEMU-2.7 and probably not 2.11 material this late
into the freeze.  A "Fixes" tag would probably also be appropriate,
identifying the commit where this was introduced (318f67ce1371) if it
is a QEMU bug.  Thanks,

Alex

> This adds a fallback to the v1 IOMMU if v2 cannot be used.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  hw/vfio/common.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 7b2924c..cd81cc9 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -1040,6 +1040,11 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as,
>              v2 ? VFIO_SPAPR_TCE_v2_IOMMU : VFIO_SPAPR_TCE_IOMMU;
>          ret = ioctl(fd, VFIO_SET_IOMMU, container->iommu_type);
>          if (ret) {
> +            container->iommu_type = VFIO_SPAPR_TCE_IOMMU;
> +            v2 = false;
> +            ret = ioctl(fd, VFIO_SET_IOMMU, container->iommu_type);
> +        }
> +        if (ret) {
>              error_setg_errno(errp, errno, "failed to set iommu for container");
>              ret = -errno;
>              goto free_container_exit;