diff mbox series

[2/4] x86/iommu: Make x86-iommu a singleton object

Message ID 20241024165627.1372621-3-peterx@redhat.com (mailing list archive)
State New
Headers show
Series QOM: Singleton interface | expand

Commit Message

Peter Xu Oct. 24, 2024, 4:56 p.m. UTC 
X86 IOMMUs cannot be created more than one on a system yet.  Make it a
singleton so it guards the system from accidentally create yet another
IOMMU object when one already presents.

Now if someone tries to create more than one, e.g., via:

  ./qemu -M q35 -device intel-iommu -device intel-iommu

The error will change from:

  qemu-system-x86_64: -device intel-iommu: QEMU does not support multiple vIOMMUs for x86 yet.

To:

  qemu-system-x86_64: -device intel-iommu: Class 'intel-iommu' only supports one instance

Unfortunately, yet we can't remove the singleton check in the machine
hook (pc_machine_device_pre_plug_cb), because there can also be
virtio-iommu involved, which doesn't share a common parent class yet.

But with this, it should be closer to reach that goal to check singleton by
QOM one day.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 hw/i386/x86-iommu.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

Comments

Markus Armbruster Oct. 25, 2024, 9:25 a.m. UTC | #1 
Peter Xu <peterx@redhat.com> writes:

> X86 IOMMUs cannot be created more than one on a system yet.  Make it a
> singleton so it guards the system from accidentally create yet another
> IOMMU object when one already presents.
>
> Now if someone tries to create more than one, e.g., via:
>
>   ./qemu -M q35 -device intel-iommu -device intel-iommu
>
> The error will change from:
>
>   qemu-system-x86_64: -device intel-iommu: QEMU does not support multiple vIOMMUs for x86 yet.
>
> To:
>
>   qemu-system-x86_64: -device intel-iommu: Class 'intel-iommu' only supports one instance
>
> Unfortunately, yet we can't remove the singleton check in the machine
> hook (pc_machine_device_pre_plug_cb), because there can also be
> virtio-iommu involved, which doesn't share a common parent class yet.
>
> But with this, it should be closer to reach that goal to check singleton by
> QOM one day.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>

$ qemu-system-x86_64 -device amd-iommu,help
/work/armbru/qemu/include/hw/boards.h:24:MACHINE: Object 0x56473906f960 is not an instance of type machine
Aborted (core dumped)

(gdb) bt
#0  0x00007ffff4e43834 in __pthread_kill_implementation () at /lib64/libc.so.6
#1  0x00007ffff4df18ee in raise () at /lib64/libc.so.6
#2  0x00007ffff4dd98ff in abort () at /lib64/libc.so.6
#3  0x0000555555f75ef3 in object_dynamic_cast_assert
    (obj=0x555557e03960, typename=0x5555563c403e "machine", file=0x5555563c4018 "/work/armbru/qemu/include/hw/boards.h", line=24, func=0x5555563c4290 <__func__.7> "MACHINE") at ../qom/object.c:936
#4  0x0000555555d5db0f in MACHINE (obj=0x555557e03960)
    at /work/armbru/qemu/include/hw/boards.h:24
#5  0x0000555555d5e030 in x86_iommu_get_default () at ../hw/i386/x86-iommu.c:83
#6  0x0000555555d5e262 in x86_iommu_get_instance
    (errp=0x5555573d4918 <error_abort>) at ../hw/i386/x86-iommu.c:139
#7  0x0000555555f7c27c in singleton_get_instance (class=0x555557e00320)
    at ../qom/object_interfaces.c:371
#8  0x000055555612a842 in qmp_device_list_properties
    (typename=0x555557e001d0 "amd-iommu", errp=0x7fffffffda38)
    at ../qom/qom-qmp-cmds.c:147
#9  0x0000555555bf20b2 in qdev_device_help (opts=0x555557e001f0)
    at ../system/qdev-monitor.c:314
#10 0x0000555555bfe06d in device_help_func
    (opaque=0x0, opts=0x555557e001f0, errp=0x0) at ../system/vl.c:1208
#11 0x0000555556217186 in qemu_opts_foreach
    (list=0x55555729e5c0 <qemu_device_opts>, func=0x555555bfe04d <device_help_func>, opaque=0x0, errp=0x0) at ../util/qemu-option.c:1135
#12 0x0000555555c01d56 in qemu_process_help_options () at ../system/vl.c:2555
#13 0x0000555555c04d81 in qemu_init (argc=3, argv=0x7fffffffde28)
    at ../system/vl.c:3654
#14 0x000055555612ffae in main (argc=3, argv=0x7fffffffde28)
    at ../system/main.c:47
Peter Xu Oct. 25, 2024, 9:55 p.m. UTC | #2 
On Fri, Oct 25, 2024 at 11:25:23AM +0200, Markus Armbruster wrote:
> Peter Xu <peterx@redhat.com> writes:
> 
> > X86 IOMMUs cannot be created more than one on a system yet.  Make it a
> > singleton so it guards the system from accidentally create yet another
> > IOMMU object when one already presents.
> >
> > Now if someone tries to create more than one, e.g., via:
> >
> >   ./qemu -M q35 -device intel-iommu -device intel-iommu
> >
> > The error will change from:
> >
> >   qemu-system-x86_64: -device intel-iommu: QEMU does not support multiple vIOMMUs for x86 yet.
> >
> > To:
> >
> >   qemu-system-x86_64: -device intel-iommu: Class 'intel-iommu' only supports one instance
> >
> > Unfortunately, yet we can't remove the singleton check in the machine
> > hook (pc_machine_device_pre_plug_cb), because there can also be
> > virtio-iommu involved, which doesn't share a common parent class yet.
> >
> > But with this, it should be closer to reach that goal to check singleton by
> > QOM one day.
> >
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> 
> $ qemu-system-x86_64 -device amd-iommu,help
> /work/armbru/qemu/include/hw/boards.h:24:MACHINE: Object 0x56473906f960 is not an instance of type machine
> Aborted (core dumped)
> 
> (gdb) bt
> #0  0x00007ffff4e43834 in __pthread_kill_implementation () at /lib64/libc.so.6
> #1  0x00007ffff4df18ee in raise () at /lib64/libc.so.6
> #2  0x00007ffff4dd98ff in abort () at /lib64/libc.so.6
> #3  0x0000555555f75ef3 in object_dynamic_cast_assert
>     (obj=0x555557e03960, typename=0x5555563c403e "machine", file=0x5555563c4018 "/work/armbru/qemu/include/hw/boards.h", line=24, func=0x5555563c4290 <__func__.7> "MACHINE") at ../qom/object.c:936
> #4  0x0000555555d5db0f in MACHINE (obj=0x555557e03960)
>     at /work/armbru/qemu/include/hw/boards.h:24
> #5  0x0000555555d5e030 in x86_iommu_get_default () at ../hw/i386/x86-iommu.c:83
> #6  0x0000555555d5e262 in x86_iommu_get_instance
>     (errp=0x5555573d4918 <error_abort>) at ../hw/i386/x86-iommu.c:139
> #7  0x0000555555f7c27c in singleton_get_instance (class=0x555557e00320)
>     at ../qom/object_interfaces.c:371
> #8  0x000055555612a842 in qmp_device_list_properties
>     (typename=0x555557e001d0 "amd-iommu", errp=0x7fffffffda38)
>     at ../qom/qom-qmp-cmds.c:147
> #9  0x0000555555bf20b2 in qdev_device_help (opts=0x555557e001f0)
>     at ../system/qdev-monitor.c:314
> #10 0x0000555555bfe06d in device_help_func
>     (opaque=0x0, opts=0x555557e001f0, errp=0x0) at ../system/vl.c:1208
> #11 0x0000555556217186 in qemu_opts_foreach
>     (list=0x55555729e5c0 <qemu_device_opts>, func=0x555555bfe04d <device_help_func>, opaque=0x0, errp=0x0) at ../util/qemu-option.c:1135
> #12 0x0000555555c01d56 in qemu_process_help_options () at ../system/vl.c:2555
> #13 0x0000555555c04d81 in qemu_init (argc=3, argv=0x7fffffffde28)
>     at ../system/vl.c:3654
> #14 0x000055555612ffae in main (argc=3, argv=0x7fffffffde28)
>     at ../system/main.c:47
> 

Thanks for the report!

It turns out that qdev_get_machine() cannot be invoked too early, and the
singleton code can make it earlier..

We may want a pre-requisite patch to allow qdev_get_machine() to be invoked
anytime, like:

===8<===
diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index db36f54d91..7ceae47139 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -831,6 +831,16 @@ Object *qdev_get_machine(void)
 {
     static Object *dev;
 
+    if (!phase_check(PHASE_MACHINE_CREATED)) {
+        /*
+         * When the machine is not created, below can wrongly create
+         * /machine to be a container.. this enables qdev_get_machine() to
+         * be used at any time and return NULL properly when machine is not
+         * created.
+         */
+        return NULL;
+    }
+
     if (dev == NULL) {
         dev = container_get(object_get_root(), "/machine");
     }
===8<===

I hope it makes sense on its own. Then callers who can be invoked earlier
could then handle NULL properly, in this case..

===8<===
diff --git a/hw/i386/x86-iommu.c b/hw/i386/x86-iommu.c
index 4bfeb08705..fceb7adfe0 100644
--- a/hw/i386/x86-iommu.c
+++ b/hw/i386/x86-iommu.c
@@ -80,9 +80,15 @@ void x86_iommu_irq_to_msi_message(X86IOMMUIrq *irq, MSIMessage *msg_out)
 
 X86IOMMUState *x86_iommu_get_default(void)
 {
-    MachineState *ms = MACHINE(qdev_get_machine());
-    PCMachineState *pcms =
-        PC_MACHINE(object_dynamic_cast(OBJECT(ms), TYPE_PC_MACHINE));
+    Object *machine = qdev_get_machine();
+    PCMachineState *pcms;
+
+    /* If machine has not been created, so is the vIOMMU */
+    if (!machine) {
+        return NULL;
+    }
+
+    pcms = PC_MACHINE(object_dynamic_cast(machine, TYPE_PC_MACHINE));
 
     if (pcms &&
         object_dynamic_cast(OBJECT(pcms->iommu), TYPE_X86_IOMMU_DEVICE)) {
===8<===

I'll make sure this works if I'll repost.

Thanks,
Peter Xu Oct. 25, 2024, 10:13 p.m. UTC | #3 
On Fri, Oct 25, 2024 at 05:55:59PM -0400, Peter Xu wrote:
> On Fri, Oct 25, 2024 at 11:25:23AM +0200, Markus Armbruster wrote:
> > Peter Xu <peterx@redhat.com> writes:
> > 
> > > X86 IOMMUs cannot be created more than one on a system yet.  Make it a
> > > singleton so it guards the system from accidentally create yet another
> > > IOMMU object when one already presents.
> > >
> > > Now if someone tries to create more than one, e.g., via:
> > >
> > >   ./qemu -M q35 -device intel-iommu -device intel-iommu
> > >
> > > The error will change from:
> > >
> > >   qemu-system-x86_64: -device intel-iommu: QEMU does not support multiple vIOMMUs for x86 yet.
> > >
> > > To:
> > >
> > >   qemu-system-x86_64: -device intel-iommu: Class 'intel-iommu' only supports one instance
> > >
> > > Unfortunately, yet we can't remove the singleton check in the machine
> > > hook (pc_machine_device_pre_plug_cb), because there can also be
> > > virtio-iommu involved, which doesn't share a common parent class yet.
> > >
> > > But with this, it should be closer to reach that goal to check singleton by
> > > QOM one day.
> > >
> > > Signed-off-by: Peter Xu <peterx@redhat.com>
> > 
> > $ qemu-system-x86_64 -device amd-iommu,help
> > /work/armbru/qemu/include/hw/boards.h:24:MACHINE: Object 0x56473906f960 is not an instance of type machine
> > Aborted (core dumped)
> > 
> > (gdb) bt
> > #0  0x00007ffff4e43834 in __pthread_kill_implementation () at /lib64/libc.so.6
> > #1  0x00007ffff4df18ee in raise () at /lib64/libc.so.6
> > #2  0x00007ffff4dd98ff in abort () at /lib64/libc.so.6
> > #3  0x0000555555f75ef3 in object_dynamic_cast_assert
> >     (obj=0x555557e03960, typename=0x5555563c403e "machine", file=0x5555563c4018 "/work/armbru/qemu/include/hw/boards.h", line=24, func=0x5555563c4290 <__func__.7> "MACHINE") at ../qom/object.c:936
> > #4  0x0000555555d5db0f in MACHINE (obj=0x555557e03960)
> >     at /work/armbru/qemu/include/hw/boards.h:24
> > #5  0x0000555555d5e030 in x86_iommu_get_default () at ../hw/i386/x86-iommu.c:83
> > #6  0x0000555555d5e262 in x86_iommu_get_instance
> >     (errp=0x5555573d4918 <error_abort>) at ../hw/i386/x86-iommu.c:139
> > #7  0x0000555555f7c27c in singleton_get_instance (class=0x555557e00320)
> >     at ../qom/object_interfaces.c:371
> > #8  0x000055555612a842 in qmp_device_list_properties
> >     (typename=0x555557e001d0 "amd-iommu", errp=0x7fffffffda38)
> >     at ../qom/qom-qmp-cmds.c:147
> > #9  0x0000555555bf20b2 in qdev_device_help (opts=0x555557e001f0)
> >     at ../system/qdev-monitor.c:314
> > #10 0x0000555555bfe06d in device_help_func
> >     (opaque=0x0, opts=0x555557e001f0, errp=0x0) at ../system/vl.c:1208
> > #11 0x0000555556217186 in qemu_opts_foreach
> >     (list=0x55555729e5c0 <qemu_device_opts>, func=0x555555bfe04d <device_help_func>, opaque=0x0, errp=0x0) at ../util/qemu-option.c:1135
> > #12 0x0000555555c01d56 in qemu_process_help_options () at ../system/vl.c:2555
> > #13 0x0000555555c04d81 in qemu_init (argc=3, argv=0x7fffffffde28)
> >     at ../system/vl.c:3654
> > #14 0x000055555612ffae in main (argc=3, argv=0x7fffffffde28)
> >     at ../system/main.c:47
> > 
> 
> Thanks for the report!
> 
> It turns out that qdev_get_machine() cannot be invoked too early, and the
> singleton code can make it earlier..
> 
> We may want a pre-requisite patch to allow qdev_get_machine() to be invoked
> anytime, like:
> 
> ===8<===
> diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> index db36f54d91..7ceae47139 100644
> --- a/hw/core/qdev.c
> +++ b/hw/core/qdev.c
> @@ -831,6 +831,16 @@ Object *qdev_get_machine(void)
>  {
>      static Object *dev;
>  
> +    if (!phase_check(PHASE_MACHINE_CREATED)) {
> +        /*
> +         * When the machine is not created, below can wrongly create
> +         * /machine to be a container.. this enables qdev_get_machine() to
> +         * be used at any time and return NULL properly when machine is not
> +         * created.
> +         */
> +        return NULL;
> +    }
> +
>      if (dev == NULL) {
>          dev = container_get(object_get_root(), "/machine");
>      }
> ===8<===
> 
> I hope it makes sense on its own.

My apologies, spoke too soon here.  This helper is used too after machine
is created, but right before switching to PHASE_MACHINE_CREATE stage..

So we need another way, like:

===8<===
diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index db36f54d91..36a9fdb428 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -832,7 +832,13 @@ Object *qdev_get_machine(void)
     static Object *dev;
 
     if (dev == NULL) {
-        dev = container_get(object_get_root(), "/machine");
+        /*
+         * NOTE: dev can keep being NULL if machine is not yet created!
+         * In which case the function will properly return NULL.
+         *
+         * Whenever machine object is created and found once, we cache it.
+         */
+        dev = object_resolve_path_component(object_get_root(), "machine");
     }
 
     return dev;
===8<===

The idea is still the same.  Meanwhile I'll test more to see whether it has
other issues.

Thanks,

> Then callers who can be invoked earlier
> could then handle NULL properly, in this case..
> 
> ===8<===
> diff --git a/hw/i386/x86-iommu.c b/hw/i386/x86-iommu.c
> index 4bfeb08705..fceb7adfe0 100644
> --- a/hw/i386/x86-iommu.c
> +++ b/hw/i386/x86-iommu.c
> @@ -80,9 +80,15 @@ void x86_iommu_irq_to_msi_message(X86IOMMUIrq *irq, MSIMessage *msg_out)
>  
>  X86IOMMUState *x86_iommu_get_default(void)
>  {
> -    MachineState *ms = MACHINE(qdev_get_machine());
> -    PCMachineState *pcms =
> -        PC_MACHINE(object_dynamic_cast(OBJECT(ms), TYPE_PC_MACHINE));
> +    Object *machine = qdev_get_machine();
> +    PCMachineState *pcms;
> +
> +    /* If machine has not been created, so is the vIOMMU */
> +    if (!machine) {
> +        return NULL;
> +    }
> +
> +    pcms = PC_MACHINE(object_dynamic_cast(machine, TYPE_PC_MACHINE));
>  
>      if (pcms &&
>          object_dynamic_cast(OBJECT(pcms->iommu), TYPE_X86_IOMMU_DEVICE)) {
> ===8<===
> 
> I'll make sure this works if I'll repost.
> 
> Thanks,
> 
> -- 
> Peter Xu
diff mbox series

Patch

diff --git a/hw/i386/x86-iommu.c b/hw/i386/x86-iommu.c
index 60af896225..4bfeb08705 100644
--- a/hw/i386/x86-iommu.c
+++ b/hw/i386/x86-iommu.c
@@ -26,6 +26,7 @@ 
 #include "qemu/error-report.h"
 #include "trace.h"
 #include "sysemu/kvm.h"
+#include "qom/object_interfaces.h"
 
 void x86_iommu_iec_register_notifier(X86IOMMUState *iommu,
                                      iec_notify_fn fn, void *data)
@@ -133,10 +134,19 @@  static Property x86_iommu_properties[] = {
     DEFINE_PROP_END_OF_LIST(),
 };
 
+static Object *x86_iommu_get_instance(Error **errp)
+{
+    return OBJECT(x86_iommu_get_default());
+}
+
 static void x86_iommu_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
+    SingletonClass *singleton = SINGLETON_CLASS(klass);
+
     dc->realize = x86_iommu_realize;
+    singleton->get_instance = x86_iommu_get_instance;
+
     device_class_set_props(dc, x86_iommu_properties);
 }
 
@@ -152,6 +162,10 @@  static const TypeInfo x86_iommu_info = {
     .class_init    = x86_iommu_class_init,
     .class_size    = sizeof(X86IOMMUClass),
     .abstract      = true,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_SINGLETON },
+        { }
+    }
 };
 
 static void x86_iommu_register_types(void)