Re: [Qemu-devel] [PATCH qemu v2 2/2] spapr_pci: Remove constraints about VFIO-PCI devices

[Alex Williamson]

On Wed, 2015-09-09 at 20:43 -0600, Alex Williamson wrote:
> On Thu, 2015-09-03 at 14:40 +1000, Alexey Kardashevskiy wrote:
> > So far there were 2 limitations enforced on an emulated PHB
> > regarding VFIO:
> > 1) only one IOMMU group per IOMMU container was allowed and
> > the spapr-pci-vfio-host-bridge device has an IOMMU ID property for this;
> > 2) only one IOMMU container per PHB was allowed as a group
> > can only be attached to one container.
> > 
> > However these are not really necessary so we are removing them here.
> > 
> > This deprecates IOMMU group ID and changes vfio_container_do_ioctl()
> > not to receive it. Instead of getting a container from a group ID,
> > this calls ioctl() for every container attached to the PHB address space.
> > This allows multiple containers on the same PHB which means multiple
> > groups per PHB. Note that this will lead to every H_PUT_TCE&etc call
> > to be passed to every container separately which will affect
> > the performance. For 32bit devices it is still recommended to put
> > every group to a separate PHB.
> > 
> > Since the existing VFIO code is already trying to share a container for
> > multiple groups, just removing a group id from
> > the vfio_container_do_ioctl() allows the existing code to share
> > a container if it is supported by the host kernel.
> > 
> > This replaces the check for a group id to be set correctly with
> > the check that it is not set.
> > 
> > This removes casts to sPAPRPHBVFIOState as none of sPAPRPHBVFIOState
> > members is accessed here.
> > 
> > Signed-off-by: Alexey Kardashevskiy <address@hidden>
> > ---
> >  hw/ppc/spapr_pci.c      | 10 +++++-----
> >  hw/ppc/spapr_pci_vfio.c | 17 ++++++-----------
> >  hw/vfio/common.c        | 22 ++++++----------------
> >  include/hw/vfio/vfio.h  |  3 +--
> >  4 files changed, 18 insertions(+), 34 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> > index 4e289cb..1b7559d 100644
> > --- a/hw/ppc/spapr_pci.c
> > +++ b/hw/ppc/spapr_pci.c
> > @@ -810,11 +810,6 @@ static int 
> > spapr_phb_dma_capabilities_update(sPAPRPHBState *sphb)
> >      pci_for_each_device(bus, pci_bus_num(bus), spapr_phb_walk_devices, 
> > sphb);
> >  
> >      if (sphb->vfio_num) {
> > -        if (sphb->iommugroupid == -1) {
> > -            error_report("Wrong IOMMU group ID %d", sphb->iommugroupid);
> > -            return -1;
> > -        }
> > -
> >          ret = spapr_phb_vfio_dma_capabilities_update(sphb);
> >          if (ret) {
> >              error_report("Unable to get DMA32 info from VFIO");
> > @@ -1282,6 +1277,11 @@ static void spapr_phb_realize(DeviceState *dev, 
> > Error **errp)
> >      PCIBus *bus;
> >      uint64_t msi_window_size = 4096;
> >  
> > +    if ((sphb->iommugroupid != -1) &&
> > +        object_dynamic_cast(OBJECT(sphb), 
> > TYPE_SPAPR_PCI_VFIO_HOST_BRIDGE)) {
> > +        error_report("Warning: iommugroupid is deprecated and will be 
> > ignored");
> > +    }
> > +
> >      if (sphb->index != (uint32_t)-1) {
> >          hwaddr windows_base;
> >  
> > diff --git a/hw/ppc/spapr_pci_vfio.c b/hw/ppc/spapr_pci_vfio.c
> > index f94d8a4..48137d5 100644
> > --- a/hw/ppc/spapr_pci_vfio.c
> > +++ b/hw/ppc/spapr_pci_vfio.c
> > @@ -35,7 +35,7 @@ int spapr_phb_vfio_dma_capabilities_update(sPAPRPHBState 
> > *sphb)
> >      struct vfio_iommu_spapr_tce_info info = { .argsz = sizeof(info) };
> >      int ret;
> >  
> > -    ret = vfio_container_ioctl(&sphb->iommu_as, sphb->iommugroupid,
> > +    ret = vfio_container_ioctl(&sphb->iommu_as,
> >                                 VFIO_IOMMU_SPAPR_TCE_GET_INFO, &info);
> >      if (ret) {
> >          return ret;
> > @@ -54,8 +54,7 @@ void spapr_phb_vfio_eeh_reenable(sPAPRPHBState *sphb)
> >          .op    = VFIO_EEH_PE_ENABLE
> >      };
> >  
> > -    vfio_container_ioctl(&sphb->iommu_as,
> > -                         sphb->iommugroupid, VFIO_EEH_PE_OP, &op);
> > +    vfio_container_ioctl(&sphb->iommu_as, VFIO_EEH_PE_OP, &op);
> >  }
> >  
> >  int spapr_phb_vfio_eeh_set_option(sPAPRPHBState *sphb,
> > @@ -81,8 +80,7 @@ int spapr_phb_vfio_eeh_set_option(sPAPRPHBState *sphb,
> >          return RTAS_OUT_PARAM_ERROR;
> >      }
> >  
> > -    ret = vfio_container_ioctl(&sphb->iommu_as, sphb->iommugroupid,
> > -                               VFIO_EEH_PE_OP, &op);
> > +    ret = vfio_container_ioctl(&sphb->iommu_as, VFIO_EEH_PE_OP, &op);
> >      if (ret < 0) {
> >          return RTAS_OUT_HW_ERROR;
> >      }
> > @@ -96,8 +94,7 @@ int spapr_phb_vfio_eeh_get_state(sPAPRPHBState *sphb, int 
> > *state)
> >      int ret;
> >  
> >      op.op = VFIO_EEH_PE_GET_STATE;
> > -    ret = vfio_container_ioctl(&sphb->iommu_as, sphb->iommugroupid,
> > -                               VFIO_EEH_PE_OP, &op);
> > +    ret = vfio_container_ioctl(&sphb->iommu_as, VFIO_EEH_PE_OP, &op);
> >      if (ret < 0) {
> >          return RTAS_OUT_PARAM_ERROR;
> >      }
> > @@ -170,8 +167,7 @@ int spapr_phb_vfio_eeh_reset(sPAPRPHBState *sphb, int 
> > option)
> >          return RTAS_OUT_PARAM_ERROR;
> >      }
> >  
> > -    ret = vfio_container_ioctl(&sphb->iommu_as, sphb->iommugroupid,
> > -                               VFIO_EEH_PE_OP, &op);
> > +    ret = vfio_container_ioctl(&sphb->iommu_as, VFIO_EEH_PE_OP, &op);
> >      if (ret < 0) {
> >          return RTAS_OUT_HW_ERROR;
> >      }
> > @@ -185,8 +181,7 @@ int spapr_phb_vfio_eeh_configure(sPAPRPHBState *sphb)
> >      int ret;
> >  
> >      op.op = VFIO_EEH_PE_CONFIGURE;
> > -    ret = vfio_container_ioctl(&sphb->iommu_as, sphb->iommugroupid,
> > -                               VFIO_EEH_PE_OP, &op);
> > +    ret = vfio_container_ioctl(&sphb->iommu_as, VFIO_EEH_PE_OP, &op);
> >      if (ret < 0) {
> >          return RTAS_OUT_PARAM_ERROR;
> >      }
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index 85ee9b0..a00644e 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -926,35 +926,25 @@ void vfio_put_base_device(VFIODevice *vbasedev)
> >      close(vbasedev->fd);
> >  }
> >  
> > -static int vfio_container_do_ioctl(AddressSpace *as, int32_t groupid,
> > -                                   int req, void *param)
> > +static int vfio_container_do_ioctl(AddressSpace *as, int req, void *param)
> >  {
> > -    VFIOGroup *group;
> >      VFIOContainer *container;
> >      int ret = -1;
> > +    VFIOAddressSpace *space = vfio_get_address_space(as);
> >  
> > -    group = vfio_get_group(groupid, as);
> > -    if (!group) {
> > -        error_report("vfio: group %d not registered", groupid);
> > -        return ret;
> > -    }
> > -
> > -    container = group->container;
> > -    if (group->container) {
> > +    QLIST_FOREACH(container, &space->containers, next) {
> >          ret = ioctl(container->fd, req, param);
> >          if (ret < 0) {
> >              error_report("vfio: failed to ioctl %d to container: ret=%d, 
> > %s",
> >                           _IOC_NR(req) - VFIO_BASE, ret, strerror(errno));
> > +            return -errno;
> >          }
> >      }
> 
> This highlights how terrible this ioctl passthrough interface is; what's
> a caller supposed to do on error?  Here we don't have visibility into
> the ioctl being called in order to do any unwind on error.  The caller
> doesn't have the context to unwind only the failed containers.  Is
> returning errno here really sufficient for anyone to figure out how to
> proceed or should we just cut our loses and abort()?  What's the least
> horrible way we can realistically handle a failure here?  Thanks,

It seemed like I asked this before and it turns out that I did:

https://lists.gnu.org/archive/html/qemu-devel/2015-06/msg07399.html

"Gavin says yes" is not really a supportable solution when I stumbled on
it again and David doesn't know why it's safe either (nor does it answer
my question of how does this work).  At a minimum, the reasoning why
this is safe for the ioctls we currently allow here needs to be spelled
out in a comment.  We could easily make the mistake of adding another
ioctl to the passthrough for which those assumptions are not valid.  We
may even want to abort if it's not one of the ioctls we've evaluated so
we don't overlook this problem later.  Thanks,

Alex

>   
> > -    vfio_put_group(group);
> > -
> >      return ret;
> >  }
> >  
> > -int vfio_container_ioctl(AddressSpace *as, int32_t groupid,
> > -                         int req, void *param)
> > +int vfio_container_ioctl(AddressSpace *as, int req, void *param)
> >  {
> >      /* We allow only certain ioctls to the container */
> >      switch (req) {
> > @@ -968,5 +958,5 @@ int vfio_container_ioctl(AddressSpace *as, int32_t 
> > groupid,
> >          return -1;
> >      }
> >  
> > -    return vfio_container_do_ioctl(as, groupid, req, param);
> > +    return vfio_container_do_ioctl(as, req, param);
> >  }
> > diff --git a/include/hw/vfio/vfio.h b/include/hw/vfio/vfio.h
> > index 0b26cd8..e076c14 100644
> > --- a/include/hw/vfio/vfio.h
> > +++ b/include/hw/vfio/vfio.h
> > @@ -3,7 +3,6 @@
> >  
> >  #include "qemu/typedefs.h"
> >  
> > -extern int vfio_container_ioctl(AddressSpace *as, int32_t groupid,
> > -                                int req, void *param);
> > +extern int vfio_container_ioctl(AddressSpace *as, int req, void *param);
> >  
> >  #endif
> 
>