Hi,
On 21.08.2017 09:36, Pankaj Gupta wrote:
>
> Hello Thomas,
>>
>> QEMU currently crashes when trying to use a 'pc-dimm' on the pseries
>> machine without specifying its 'memdev' property. This happens because
>> pc_dimm_get_memory_region() does not check whether the 'memdev' property
>> has properly been set by the user. Looking closer at this function, it's
>> also obvious that it is using &error_abort to call another function - and
>> this is bad in a function that is used in the hot-plugging calling chain
>> since this can also cause QEMU to exit unexpectedly.
>
> In place of checking if 'memdev' is already allocated/present while fetching
> 'get_functions' every place. If 'memdev' is required for memory hotplug
> operation
> can we just put a check at some common place and don't start or instantiate
> if
> 'memdev' is not present.
>
> I can see:
>
> 'pc_dimm_realize' function checks for : in my case prints warning
> and avoid Qemu to start.
> ...
> ...
> if (!dimm->hostmem) {
> error_setg(errp, "'" PC_DIMM_MEMDEV_PROP "' property is not set");
> return;
> }
> ...
That check unfortunately does not apply here: The crash happens in the
pre_plug() handler of the spapr machine, and this is called *before* the
realize function of the pc-dimm is called!
But even if we could find another common place where we could check
dimm->hostmem first, you still have the problem that
host_memory_backend_get_memory() could return an error and thus
pc_dimm_get_memory_region() still needs a way to fail gracefully during
the hotplug (or also hot-unplug) operation. So I think my patch is the
right way to go here.
Thomas
