Re: [Qemu-devel] [PATCH v4 18/18] vfio: Enable in-kernel acceleration via VFIO KVM device

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Jan 29, 2015 at 08:27:30PM +1100, Alexey Kardashevskiy wrote:
> TCE hypercalls (H_PUT_TCE, H_PUT_TCE_INDIRECT, H_STUFF_TCE) use a logical bus
> number (LIOBN) to identify which TCE table the request is addressed to.
> However VFIO kernel driver operates with IOMMU group IDs and has no idea
> about which LIOBN corresponds to which group. If the host kernel supports
> in-kernel acceleration for TCE calls, we have to provide the LIOBN to IOMMU
> mapping information.
> 
> This makes use of a VFIO KVM device's
> KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN attribute to set the link
> between LIOBN and IOMMU group.
> 
> The vfio_container_spapr_set_liobn() helper is implemented completely
> in vfio.c because kvm_vfio_spapr_tce_liobn needs a group fd and
> we do not want to share resources likes that outside vfio.c.

I thought you'd moved away from the idea of in-kernel TCE
acceleration, since big DMA windows made it unnecessary.

> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  hw/ppc/spapr_iommu.c    |  1 +
>  hw/ppc/spapr_pci_vfio.c | 11 +++++++++++
>  hw/vfio/common.c        | 33 +++++++++++++++++++++++++++++++++
>  include/hw/vfio/vfio.h  |  4 ++++
>  4 files changed, 49 insertions(+)
> 
> diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
> index 258f837..3de95d7 100644
> --- a/hw/ppc/spapr_iommu.c
> +++ b/hw/ppc/spapr_iommu.c
> @@ -142,6 +142,7 @@ static int spapr_tce_table_realize(DeviceState *dev)
>      if (!tcet->table) {
>          size_t table_size = tcet->nb_table * sizeof(uint64_t);
>          tcet->table = g_malloc0(table_size);
> +        tcet->vfio_accel = false;

This should probably have a qdev prop so that it can be explicitly
disabled on a per-device basis for testing.

>      }
>  
>      trace_spapr_iommu_new_table(tcet->liobn, tcet, tcet->table, tcet->fd);
> diff --git a/hw/ppc/spapr_pci_vfio.c b/hw/ppc/spapr_pci_vfio.c
> index 257181d..2078187 100644
> --- a/hw/ppc/spapr_pci_vfio.c
> +++ b/hw/ppc/spapr_pci_vfio.c
> @@ -21,6 +21,7 @@
>  #include "hw/pci-host/spapr.h"
>  #include "linux/vfio.h"
>  #include "hw/vfio/vfio.h"
> +#include "qemu/error-report.h"
>  
>  static Property spapr_phb_vfio_properties[] = {
>      DEFINE_PROP_INT32("iommu", sPAPRPHBVFIOState, iommugroupid, -1),
> @@ -80,6 +81,16 @@ static int spapr_pci_vfio_ddw_create(sPAPRPHBState *sphb, uint32_t liobn,
>      memory_region_add_subregion(&sphb->iommu_root, (*ptcet)->bus_offset,
>                                  spapr_tce_get_iommu(*ptcet));
>  
> +    if (!(*ptcet)->vfio_accel) {
> +        return 0;
> +    }
> +    ret = vfio_container_spapr_set_liobn(&sphb->iommu_as,
> +                                         liobn, (*ptcet)->bus_offset);
> +    if (ret) {
> +        error_report("spapr-vfio: failed to create link to IOMMU");
> +        ret = 0;
> +    }
> +
>      return ret;
>  }
>  
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index a26cbae..ec778d0 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -1053,3 +1053,36 @@ int vfio_container_ioctl(AddressSpace *as,
>  
>      return vfio_container_do_ioctl(as, req, param);
>  }
> +
> +int vfio_container_spapr_set_liobn(AddressSpace *as,
> +                                   uint64_t liobn,
> +                                   uint64_t start_addr)
> +{
> +#ifdef CONFIG_KVM
> +    int ret;
> +    struct kvm_vfio_spapr_tce_liobn param = {
> +        .argsz = sizeof(param),
> +        .liobn = liobn,
> +        .start_addr = start_addr
> +    };
> +    struct kvm_device_attr attr = {
> +        .group = KVM_DEV_VFIO_GROUP,
> +        .attr = KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN,
> +        .addr = (uint64_t)(unsigned long)&param,
> +    };
> +
> +    if (vfio_kvm_device_fd < 0) {
> +        return 0;
> +    }
> +
> +    ret = ioctl(vfio_kvm_device_fd, KVM_SET_DEVICE_ATTR, &attr);
> +    if (ret) {
> +        error_report("vfio: failed to setup liobn for a group: %s",
> +                     strerror(errno));
> +    }
> +
> +    return ret;
> +#else
> +    return 0;
> +#endif
> +}
> diff --git a/include/hw/vfio/vfio.h b/include/hw/vfio/vfio.h
> index 76b5744..8457933 100644
> --- a/include/hw/vfio/vfio.h
> +++ b/include/hw/vfio/vfio.h
> @@ -6,4 +6,8 @@
>  extern int vfio_container_ioctl(AddressSpace *as,
>                                  int req, void *param);
>  
> +extern int vfio_container_spapr_set_liobn(AddressSpace *as,
> +                                          uint64_t liobn,
> +                                          uint64_t start_addr);
> +
>  #endif

-- 
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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