Re: [Qemu-devel] [PATCH v3 1/2] x86_iommu: Move machine check to x86_iommu_realize()

[Mohammed Gamal]

On Mon, 2017-09-18 at 10:13 -0300, Eduardo Habkost wrote:
> On Mon, Sep 18, 2017 at 12:14:08PM +0200, Mohammed Gamal wrote:
> > Instead of having the same error checks in vtd_realize()
> > and amdvi_realize(), move that over to the generic
> > x86_iommu_realize().
> > 
> > Signed-off-by: Mohammed Gamal <address@hidden>
> > ---
> >  hw/i386/amd_iommu.c   | 10 +---------
> >  hw/i386/intel_iommu.c | 10 +---------
> >  hw/i386/x86-iommu.c   | 12 ++++++++++++
> >  3 files changed, 14 insertions(+), 18 deletions(-)
> > 
> > diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
> > index 334938a..839f01f 100644
> > --- a/hw/i386/amd_iommu.c
> > +++ b/hw/i386/amd_iommu.c
> > @@ -1141,18 +1141,10 @@ static void amdvi_realize(DeviceState *dev, Error 
> > **err)
> >      AMDVIState *s = AMD_IOMMU_DEVICE(dev);
> >      X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(dev);
> >      MachineState *ms = MACHINE(qdev_get_machine());
> > -    MachineClass *mc = MACHINE_GET_CLASS(ms);
> >      PCMachineState *pcms =
> >          PC_MACHINE(object_dynamic_cast(OBJECT(ms), TYPE_PC_MACHINE));
> 
> This is where you shouldn't use object_dynamic_cast() because the
> code now expects pcms to never be NULL...
> 
> > -    PCIBus *bus;
> > +    PCIBus *bus = pcms->bus;
> >  
> > -    if (!pcms) {
> > -        error_setg(err, "Machine-type '%s' not supported by amd-iommu",
> > -                   mc->name);
> > -        return;
> > -    }
> > -
> > -    bus = pcms->bus;
> >      s->iotlb = g_hash_table_new_full(amdvi_uint64_hash,
> >                                       amdvi_uint64_equal, g_free, g_free);
> >  
> > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> > index 3a5bb0b..aa01812 100644
> > --- a/hw/i386/intel_iommu.c
> > +++ b/hw/i386/intel_iommu.c
> > @@ -3027,20 +3027,12 @@ static bool vtd_decide_config(IntelIOMMUState *s, 
> > Error **errp)
> >  static void vtd_realize(DeviceState *dev, Error **errp)
> >  {
> >      MachineState *ms = MACHINE(qdev_get_machine());
> > -    MachineClass *mc = MACHINE_GET_CLASS(ms);
> >      PCMachineState *pcms =
> >          PC_MACHINE(object_dynamic_cast(OBJECT(ms), TYPE_PC_MACHINE));
> 
> Same as above.
> 
> > -    PCIBus *bus;
> > +    PCIBus *bus = pcms->bus;
> >      IntelIOMMUState *s = INTEL_IOMMU_DEVICE(dev);
> >      X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(dev);
> >  
> > -    if (!pcms) {
> > -        error_setg(errp, "Machine-type '%s' not supported by intel-iommu",
> > -                   mc->name);
> > -        return;
> > -    }
> > -
> > -    bus = pcms->bus;
> >      x86_iommu->type = TYPE_INTEL;
> >  
> >      if (!vtd_decide_config(s, errp)) {
> > diff --git a/hw/i386/x86-iommu.c b/hw/i386/x86-iommu.c
> > index 293caf8..d43b08a 100644
> > --- a/hw/i386/x86-iommu.c
> > +++ b/hw/i386/x86-iommu.c
> > @@ -21,6 +21,8 @@
> >  #include "hw/sysbus.h"
> >  #include "hw/boards.h"
> >  #include "hw/i386/x86-iommu.h"
> > +#include "hw/i386/pc.h"
> > +#include "qapi/error.h"
> >  #include "qemu/error-report.h"
> >  #include "trace.h"
> >  
> > @@ -80,7 +82,17 @@ static void x86_iommu_realize(DeviceState *dev, Error 
> > **errp)
> >  {
> >      X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(dev);
> >      X86IOMMUClass *x86_class = X86_IOMMU_GET_CLASS(dev);
> > +    MachineState *ms = MACHINE(qdev_get_machine());
> > +    MachineClass *mc = MACHINE_GET_CLASS(ms);
> > +    PCMachineState *pcms = PC_MACHINE(ms);
> 
> And here is where you really need object_dynamic_cast(),
> otherwise the "if (!pcms)" check below will be useless and you'll
> get this:
> 
>   $ qemu-system-x86_64 -machine none -device intel-iommu
>   qemu/hw/i386/x86-iommu.c:87:x86_iommu_realize: Object 0x53d7d02060 is not 
> an instance of type generic-pc-machine
>   Aborted (core dumped)

This is what happens when you miss your daily Caffeine dose :)
I thought the object_dynamic_cast call was redundant and thus needs to
be removed when moving the code.

I see the correct sequence you mean now. Since the check is done in the
calling x86_iommu_realize(), the check won't be need in the callees.

I will send the fixed version shortly.
> 
> >      QLIST_INIT(&x86_iommu->iec_notifiers);
> > +
> > +    if (!pcms) {
> > +        error_setg(errp, "Machine-type '%s' not supported by IOMMU",
> > +                   mc->name);
> > +        return;
> > +    }
> > +
> >      if (x86_class->realize) {
> >          x86_class->realize(dev, errp);
> >      }
> > -- 
> > 1.8.3.1
> > 
>