Re: [PATCH v4 3/3] memory_hotplug.c: send DEVICE_UNPLUG_ERROR in acpi_memory_hotplug_write()

[Markus Armbruster]

Igor Mammedov <imammedo@redhat.com> writes:

> On Fri, 09 Jul 2021 13:25:43 +0200
> Markus Armbruster <armbru@redhat.com> wrote:
>
>> Igor Mammedov <imammedo@redhat.com> writes:
>> 
>> > On Thu, 08 Jul 2021 15:08:57 +0200
>> > Markus Armbruster <armbru@redhat.com> wrote:
>> >  
>> >> Daniel Henrique Barboza <danielhb413@gmail.com> writes:
>> >>   
>> >> > MEM_UNPLUG_ERROR is deprecated since the introduction of
>> >> > DEVICE_UNPLUG_ERROR. Keep emitting both while the deprecation of
>> >> > MEM_UNPLUG_ERROR is pending.
>> >> >
>> >> > CC: Michael S. Tsirkin <mst@redhat.com>
>> >> > CC: Igor Mammedov <imammedo@redhat.com>
>> >> > Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
>> >> > Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
>> >> > ---
>> >> >  hw/acpi/memory_hotplug.c | 13 +++++++++++--
>> >> >  1 file changed, 11 insertions(+), 2 deletions(-)
>> >> >
>> >> > diff --git a/hw/acpi/memory_hotplug.c b/hw/acpi/memory_hotplug.c
>> >> > index af37889423..fb9f4d2de7 100644
>> >> > --- a/hw/acpi/memory_hotplug.c
>> >> > +++ b/hw/acpi/memory_hotplug.c
>> >> > @@ -8,6 +8,7 @@
>> >> >  #include "qapi/error.h"
>> >> >  #include "qapi/qapi-events-acpi.h"
>> >> >  #include "qapi/qapi-events-machine.h"
>> >> > +#include "qapi/qapi-events-qdev.h"
>> >> >  
>> >> >  #define MEMORY_SLOTS_NUMBER          "MDNR"
>> >> >  #define MEMORY_HOTPLUG_IO_REGION     "HPMR"
>> >> > @@ -177,9 +178,17 @@ static void acpi_memory_hotplug_write(void 
>> >> > *opaque, hwaddr addr, uint64_t data,
>> >> >              /* call pc-dimm unplug cb */
>> >> >              hotplug_handler_unplug(hotplug_ctrl, dev, &local_err);
>> >> >              if (local_err) {
>> >> > +                const char *error_pretty = error_get_pretty(local_err);
>> >> > +
>> >> >                  trace_mhp_acpi_pc_dimm_delete_failed(mem_st->selector);
>> >> > -                qapi_event_send_mem_unplug_error(dev->id,
>> >> > -                                                 
>> >> > error_get_pretty(local_err));
>> >> > +
>> >> > +                /*
>> >> > +                 * Send both MEM_UNPLUG_ERROR and DEVICE_UNPLUG_ERROR
>> >> > +                 * while the deprecation of MEM_UNPLUG_ERROR is
>> >> > +                 * pending.
>> >> > +                 */
>> >> > +                qapi_event_send_mem_unplug_error(dev->id, 
>> >> > error_pretty);
>> >> > +                qapi_event_send_device_unplug_error(dev->id, 
>> >> > error_pretty);
>> >> >                  error_free(local_err);
>> >> >                  break;
>> >> >              }    
>> >> 
>> >> Same question as for PATCH 2: can dev->id be null?  
>> > only theoretically (if memory device were created directly without
>> > using device_add), which as far as I know is not the case as all
>> > memory devices are created using -device/device_add so far.
>> >
>> > ( for device_add case see qdev_device_add->qdev_set_id where
>> >   'id' is set to user provided or to generated "device[%d]" value)  
>> 
>> Something is set to a generated value, but it's not dev->id :)
>> 
>>     void qdev_set_id(DeviceState *dev, const char *id)
>> 
>> @id is the value of id=...  It may be null.
>> 
>> dev->id still is null here.
>> 
>>     {
>>         if (id) {
>>             dev->id = id;
>>         }
>> 
>> dev->id is now the value of id=...  It may be null.
>> 
>>         if (dev->id) {
>>             object_property_add_child(qdev_get_peripheral(), dev->id,
>>                                       OBJECT(dev));
>> 
>> If the user specified id=..., add @dev as child of /peripheral.  The
>> child's name is the (non-null) value of id=...
>> 
>>         } else {
>>             static int anon_count;
>>             gchar *name = g_strdup_printf("device[%d]", anon_count++);
>>             object_property_add_child(qdev_get_peripheral_anon(), name,
>>                                       OBJECT(dev));
>>             g_free(name);
>> 
>> Else, add @dev as child of /peripheral-anon.  The child's name is made
>> up.
>> 
>> 
>>         }
>>     }
>> 
>> dev->id is still the value of id=..., i.e. it may be null.
> yep, I was wrong and confused it child name in QOM tree.
>
>> Sure dereferencing dev->id in acpi_memory_hotplug_write() is safe?
>
> it aren't safe since guest may trigger this error when
> memory-device is created without id.

Thanks!

Daniel, the issue predates your series, but your series adds instances.
We need a patch fixing the existing instances before your series, and
fix up your series.  Can you take care of that?