RE: [PATCH v2 03/22] vfio: check VFIO_TYPE1_NESTING_IOMMU support

[Liu, Yi L]

Eric,

> From: Auger Eric <address@hidden>
> Sent: Monday, March 30, 2020 5:36 PM
> To: Liu, Yi L <address@hidden>; address@hidden;
> Subject: Re: [PATCH v2 03/22] vfio: check VFIO_TYPE1_NESTING_IOMMU support
> 
> Yi,
> 
> On 3/30/20 6:24 AM, Liu Yi L wrote:
> > VFIO needs to check VFIO_TYPE1_NESTING_IOMMU support with Kernel before
> > further using it. e.g. requires to check IOMMU UAPI version.
> >
> > Cc: Kevin Tian <address@hidden>
> > Cc: Jacob Pan <address@hidden>
> > Cc: Peter Xu <address@hidden>
> > Cc: Eric Auger <address@hidden>
> > Cc: Yi Sun <address@hidden>
> > Cc: David Gibson <address@hidden>
> > Cc: Alex Williamson <address@hidden>
> > Signed-off-by: Liu Yi L <address@hidden>
> > Signed-off-by: Yi Sun <address@hidden>
> > ---
> >  hw/vfio/common.c | 14 ++++++++++++--
> >  1 file changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index 0b3593b..c276732 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -1157,12 +1157,21 @@ static void
> vfio_put_address_space(VFIOAddressSpace *space)
> >  static int vfio_get_iommu_type(VFIOContainer *container,
> >                                 Error **errp)
> >  {
> > -    int iommu_types[] = { VFIO_TYPE1v2_IOMMU, VFIO_TYPE1_IOMMU,
> > +    int iommu_types[] = { VFIO_TYPE1_NESTING_IOMMU,
> > +                          VFIO_TYPE1v2_IOMMU, VFIO_TYPE1_IOMMU,
> >                            VFIO_SPAPR_TCE_v2_IOMMU, VFIO_SPAPR_TCE_IOMMU };
> > -    int i;
> > +    int i, version;
> >
> >      for (i = 0; i < ARRAY_SIZE(iommu_types); i++) {
> >          if (ioctl(container->fd, VFIO_CHECK_EXTENSION, iommu_types[i])) {
> > +            if (iommu_types[i] == VFIO_TYPE1_NESTING_IOMMU) {
> > +                version = ioctl(container->fd, VFIO_CHECK_EXTENSION,
> > +                                VFIO_NESTING_IOMMU_UAPI);
> > +                if (version < IOMMU_UAPI_VERSION) {
> > +                    info_report("IOMMU UAPI incompatible for nesting");
> > +                    continue;
> > +                }
> > +            }
> This means that by default VFIO_TYPE1_NESTING_IOMMU wwould be chosen. I
> don't think this what we want. On ARM this would mean that for a
> standard VFIO assignment without vIOMMU, SL will be used instead of FL.
> This may not be harmless.
> 
> For instance, in "[RFC v6 09/24] vfio: Force nested if iommu requires
> it", I use nested only if I detect we have a vSMMU. Otherwise I keep the
> legacy VFIO_TYPE1v2_IOMMU.
> 
Good point. I also replied in your patch.

Regards,
Yi Liu