• Alexey Kardashevskiy's avatar
    KVM: PPC: VFIO: Add in-kernel acceleration for VFIO · 121f80ba
    Alexey Kardashevskiy authored
    This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
    and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
    without passing them to user space which saves time on switching
    to user space and back.
    
    This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
    KVM tries to handle a TCE request in the real mode, if failed
    it passes the request to the virtual mode to complete the operation.
    If it a virtual mode handler fails, the request is passed to
    the user space; this is not expected to happen though.
    
    To avoid dealing with page use counters (which is tricky in real mode),
    this only accelerates SPAPR TCE IOMMU v2 clients which are required
    to pre-register the userspace memory. The very first TCE request will
    be handled in the VFIO SPAPR TCE driver anyway as the userspace view
    of the TCE table (iommu_table::it_userspace) is not allocated till
    the very first mapping happens and we cannot call vmalloc in real mode.
    
    If we fail to update a hardware IOMMU table unexpected reason, we just
    clear it and move on as there is nothing really we can do about it -
    for example, if we hot plug a VFIO device to a guest, existing TCE tables
    will be mirrored automatically to the hardware and there is no interface
    to report to the guest about possible failures.
    
    This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
    the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
    and associates a physical IOMMU table with the SPAPR TCE table (which
    is a guest view of the hardware IOMMU table). The iommu_table object
    is cached and referenced so we do not have to look up for it in real mode.
    
    This does not implement the UNSET counterpart as there is no use for it -
    once the acceleration is enabled, the existing userspace won't
    disable it unless a VFIO container is destroyed; this adds necessary
    cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.
    
    This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
    space.
    
    This adds real mode version of WARN_ON_ONCE() as the generic version
    causes problems with rcu_sched. Since we testing what vmalloc_to_phys()
    returns in the code, this also adds a check for already existing
    vmalloc_to_phys() call in kvmppc_rm_h_put_tce_indirect().
    
    This finally makes use of vfio_external_user_iommu_id() which was
    introduced quite some time ago and was considered for removal.
    
    Tests show that this patch increases transmission speed from 220MB/s
    to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
    Signed-off-by: default avatarAlexey Kardashevskiy <aik@ozlabs.ru>
    Acked-by: default avatarAlex Williamson <alex.williamson@redhat.com>
    Reviewed-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
    Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
    121f80ba
vfio.txt 1.14 KB