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

[David Gibson]

On Wed, Nov 22, 2017 at 04:15:52PM +1100, Alexey Kardashevskiy 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.
> 
> This adds a fallback to the v1 IOMMU if v2 cannot be used.
> 
> Signed-off-by: Alexey Kardashevskiy <address@hidden>

The fallback itself isn't a bad idea, but your commit message contains
several inaccurracies.  KVM PR is not particularly designed to work in
a paravirtualized system, and it doesn't only support the pseries
platform (as guest *or* host).  It's actually a lot more general than
KVM HV - just slow, not that well tested and missing a number of
features that no-one's bothered to port to it.

> ---
>  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;

-- 
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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