Re: [Qemu-ppc] [PATCH 3/4] spapr_iommu: Provide a function to switch a TCE table to allowing VFIO

[Thomas Huth]

On 30/09/15 05:48, David Gibson wrote:
> Because of the way non-VFIO guest IOMMU operations are KVM accelerated, not
> all TCE tables (guest IOMMU contexts) can support VFIO devices.  Currently,
> this is decided at creation time.
> 
> To support hotplug of VFIO devices, we need to allow a TCE table which
> previously didn't allow VFIO devices to be switched so that it can.  This
> patch adds an spapr_tce_set_need_vfio() function to do this, by
> reallocating the table in userspace if necessary.
> 
> Currently this doesn't allow the KVM acceleration to be re-enabled if all
> the VFIO devices are removed.  That's an optimization for another time.
> 
> Signed-off-by: David Gibson <address@hidden>
> ---
>  hw/ppc/spapr_iommu.c   | 32 ++++++++++++++++++++++++++++++++
>  include/hw/ppc/spapr.h |  2 ++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
> index 5166cde..8d60f8b 100644
> --- a/hw/ppc/spapr_iommu.c
> +++ b/hw/ppc/spapr_iommu.c
> @@ -168,6 +168,38 @@ static int spapr_tce_table_realize(DeviceState *dev)
>      return 0;
>  }
>  
> +void spapr_tce_set_need_vfio(sPAPRTCETable *tcet, bool need_vfio)
> +{
> +    size_t table_size = tcet->nb_table * sizeof(uint64_t);
> +    void *newtable;
> +
> +    if (need_vfio == tcet->need_vfio) {
> +        /* Nothing to do */
> +        return;
> +    }
> +
> +    if (!need_vfio) {
> +        /* FIXME: We don't support transition back to KVM accelerated
> +         * TCEs yet */
> +        return;
> +    }
> +
> +    tcet->need_vfio = true;
> +
> +    if (tcet->fd < 0) {
> +        /* Table is already in userspace, nothing to be do */
> +        return;
> +    }
> +
> +    newtable = g_malloc0(table_size);

Since you immediately fill the whole table with the memcpy below, you do
not need to zero the memory here, i.e. g_malloc instead of g_malloc0
should be sufficient.

> +    memcpy(newtable, tcet->table, table_size);
> +
> +    kvmppc_remove_spapr_tce(tcet->table, tcet->fd, tcet->nb_table);
> +
> +    tcet->fd = -1;
> +    tcet->table = newtable;
> +}

 Thomas