Re: [Qemu-devel] [RFC PATCH 11/14] spapr_pci: Allow EEH on spapr-pci-host-bridge

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

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On Wed, Sep 23, 2015 at 08:19:36PM -0600, Alex Williamson wrote:
> On Thu, 2015-09-24 at 11:49 +1000, David Gibson wrote:
> > On Wed, Sep 23, 2015 at 11:28:01AM -0600, Alex Williamson wrote:
> > > On Sat, 2015-09-19 at 17:18 +1000, David Gibson wrote:
> > > > The pseries machine type has two variants of the PCI Host Bridge device:
> > > > spapr-pci-host-bridge and spapr-pci-vfio-host-bridge.  Originally, only the
> > > > latter could support VFIO devices, but we've now extended the VFIO code so
> > > > that they both can.
> > > > 
> > > > However, it's still only spapr-pci-vfio-host-bridge which supports the PAPR
> > > > Enhanced Error Handling (EEH) interfaces.  The reason is that we don't yet
> > > > have a way to determine the correct VFIOGroup for EEH operations on the
> > > > "plain" host bridge.
> > > > 
> > > > Handling this in general is problematic due to some limitations in the
> > > > current code, and some bugs in the kernel EEH interfaces.  However, it's
> > > > easy enough to do for the unambiguous case: where there is only one VFIO
> > > > group used on the whole host bridge i.e. one Partitionable Endpoint (PE).
> > > > 
> > > > This re-implements spapr_phb_check_vfio_group() in terms of the host
> > > > bridge's Partitionable Endpoints, allowing EEH on any host bridge in the
> > > > unambiguous case.  This is enough to make spapr-pci-host-bridge support
> > > > EEH as well as spapr-pci-vfio-host-bridge, since the latter only supported
> > > > devices from one IOMMU group anyway (although it didn't properly
> > > > enforce that).
> > > > 
> > > > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > > > ---
> > > >  hw/ppc/spapr_pci.c          | 36 ++++++++++++++++++++++++++++++++++++
> > > >  hw/ppc/spapr_pci_vfio.c     | 18 ------------------
> > > >  include/hw/pci-host/spapr.h |  1 -
> > > >  3 files changed, 36 insertions(+), 19 deletions(-)
> > > > 
> > > > diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> > > > index 81ad3ae..5614b45 100644
> > > > --- a/hw/ppc/spapr_pci.c
> > > > +++ b/hw/ppc/spapr_pci.c
> > > > @@ -41,6 +41,8 @@
> > > >  #include "hw/ppc/spapr_drc.h"
> > > >  #include "sysemu/device_tree.h"
> > > >  
> > > > +#include "hw/vfio/vfio-common.h"
> > > > +
> > > >  /* Copied from the kernel arch/powerpc/platforms/pseries/msi.c */
> > > >  #define RTAS_QUERY_FN           0
> > > >  #define RTAS_CHANGE_FN          1
> > > > @@ -446,6 +448,40 @@ static sPAPRPHBGuestPE *spapr_phb_pe_by_device(sPAPRPHBState *phb,
> > > >      return pe;
> > > >  }
> > > >  
> > > > +static int spapr_phb_check_vfio_group(sPAPRPHBState *phb, VFIOGroup **gpp)
> > > > +{
> > > > +    sPAPRPHBGuestPE *pe;
> > > > +
> > > > +    if (QLIST_EMPTY(&phb->pe_list)) {
> > > > +        /* No EEH capable devices on this PHB */
> > > > +        return RTAS_OUT_PARAM_ERROR;
> > > > +    }
> > > > +
> > > > +    /* Limitations in both qemu and the kernel mean that, for now, EEH
> > > > +     * won't work if there are devices from more than one PE
> > > > +     * (i.e. IOMMU group) on the same PHB */
> > > > +    pe = QLIST_FIRST(&phb->pe_list);
> > > > +    if (QLIST_NEXT(pe, list)) {
> > > > +        error_report("spapr-pci-host-bridge: EEH attempted on PHB with multiple"
> > > > +                     " IOMMU groups");
> > > 
> > > Don't wrap lines with search-able strings
> > 
> > Noted.
> > 
> > > > +        return RTAS_OUT_HW_ERROR;
> > > > +    }
> > > > +
> > > > +    if (!object_dynamic_cast(OBJECT(phb), "spapr-pci-vfio-host-bridge")) {
> > > > +        sPAPRPHBVFIOState *svphb = SPAPR_PCI_VFIO_HOST_BRIDGE(phb);
> > > > +        /* FIXME: this is an abstraction violation */
> > > > +        if (pe->group->groupid != svphb->iommugroupid) {
> > > > +            error_report("spapr-pci-vfio-host-bridge: Bad IOMMU group");
> > > > +            return RTAS_OUT_HW_ERROR;
> > > > +        }
> > > > +    }
> > > > +
> > > > +    if (gpp) {
> > > > +        *gpp = pe->group;
> > > > +    }
> > > > +    return RTAS_OUT_SUCCESS;
> > > 
> > > 
> > > The structure of this function finally makes some sense once we get
> > > here.
> > 
> > Yeah, I started off with something more like what you suggested in
> > earlier comments, but I changed to this rather awkward structure to
> > avoid churning the callers as this moves towards its final form
> > 
> > > I'm still not sure whether RTAS error codes make sense though,
> > > but it's just a nit.
> > 
> > Well, (nearly) all the callers are in RTAS, and translating the error
> > codes there seems pretty ugly too.
> > 
> > > I'd still prefer the function was renamed, "check"
> > > indicates a verification, not a return.  The primary purpose of calling
> > > this function is to get a group, not simply to check the validity.
> > 
> > Yeah, it's a crap name.  How about spapr_phb_find_vfio_group().
> 
> Why not just spapr_phb_get_vfio_group() since this started out as just a
> wrapper for vfio_get_group() and that's still what it's doing even
> though it's now cached on sPAPRPHBGuestPE rather than retrieved each
> time.

Well, "get" often implies taking a persistent reference in some way,
which is why I avoided it.

-- 
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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