Re: [Qemu-devel] [RFC PATCH] spapr-vty: workaround "reg" property for old kernels

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 10/16/2013 02:03 AM, Alexander Graf wrote:
> On 10/15/2013 10:50 AM, Alexey Kardashevskiy wrote:
>> Old kernels (<  3.1) handle hvcX devices different in different parts.
>> Sometime the kernel assumes that the hvc device numbers start from zero
>> and if there is just one hvc, then it is hvc0.
>>
>> However kernel's add_preferred_console() uses the very last byte of
>> the VTY's "reg" property as an hvc number so it might end up with something
>> different than hvc.
>>
>> The problem appears on SLES11SP3 and RHEL6. If to run QEMU without
>> -nodefaults, then the default VTY is created first on a VIO bus and gets
>> reg==0x71000000 so it will be hvc0 and everything will be fine.
>> If to run QEMU with:
>>   -nodefaults \
>>   -chardev "socket,id=char1,host=localhost,port=8001,server,telnet,mux=on" \
>>   -device "spapr-vty,chardev=char1" \
>>   -mon "chardev=char1,mode=readline,id=mon1" \
>>
>> then the exactly the same config is expected but in this case spapr-vty
>> gets reg==0x71000001 and therefore it becomes hvc1 and lots of debug
>> output is missing. SLES11SP3 does not even boot as /dev/console is
>> redirected to /dev/hvc0 which is dead.
>>
>> The issue can be solved by manual selection of VTY's "reg" property to
>> have last byte equal to zero.
>>
>> The alternative would be to use separate "reg" property counter for
>> automatic "reg" property generation and this is what the patch does.
>>
>> Signed-off-by: Alexey Kardashevskiy<aik@ozlabs.ru>
>> ---
>>
>> Since libvirt uses "-nodefault" a lot and in this case "spapr-nvram" gets
>> created first and gets reg=0x71000000, we cannot just ignore this. Also,
>> it does not seem an option to require libvirt users to specify spapr-vty
>> "reg" property every time.
>>
>> Can anyone think of a simpler solutionu? Thanks.
>>
>>
>> ---
>>   hw/ppc/spapr_vio.c         | 7 ++++++-
>>   include/hw/ppc/spapr_vio.h | 1 +
>>   2 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/ppc/spapr_vio.c b/hw/ppc/spapr_vio.c
>> index a6a0a51..2d56950 100644
>> --- a/hw/ppc/spapr_vio.c
>> +++ b/hw/ppc/spapr_vio.c
>> @@ -438,7 +438,11 @@ static int spapr_vio_busdev_init(DeviceState *qdev)
>>           VIOsPAPRBus *bus = DO_UPCAST(VIOsPAPRBus, bus,
>> dev->qdev.parent_bus);
>>
>>           do {
>> -            dev->reg = bus->next_reg++;
>> +            if (!object_dynamic_cast(OBJECT(qdev), "spapr-vty")) {
>> +                dev->reg = bus->next_reg++;
>> +            } else {
>> +                dev->reg = bus->next_vty_reg++;
>> +            }
>>           } while (reg_conflict(dev));
>>       }
>>
>> @@ -501,6 +505,7 @@ VIOsPAPRBus *spapr_vio_bus_init(void)
>>       qbus = qbus_create(TYPE_SPAPR_VIO_BUS, dev, "spapr-vio");
>>       bus = DO_UPCAST(VIOsPAPRBus, bus, qbus);
>>       bus->next_reg = 0x71000000;
>> +    bus->next_vty_reg = 0x71000100;
> 
> This breaks as soon as you pass in more than 0x100 devices that are non-vty
> into the guest, no?

Will we ever have this much? Ah, anyway, this code already checks if the
address is taken and fails if it is. And there is still a possibility to
assign addresses manually.

> The reg property really describes the virtual slot a device is in.

We use 0x71000000. I saw xmls from libvirt where VTY's reg is 0x30000000.
Whether it is a slot or not, QEMU/SLOF/Kernel does not seem to care about
absolute value :)

> Couldn't
> we do that allocation explicitly and push it from libvirt, just like we do
> it with the slots for PCI?

That is the other possibility, yes. But in this case "-nodefaults" must not
create spapr-nvram automatically and if we do that, we'll break existing
setups.


> 
> 
> Alex
> 
> 
>>
>>       /* hcall-vio */
>>       spapr_register_hypercall(H_VIO_SIGNAL, h_vio_signal);
>> diff --git a/include/hw/ppc/spapr_vio.h b/include/hw/ppc/spapr_vio.h
>> index d8b3b03..3a92d9e 100644
>> --- a/include/hw/ppc/spapr_vio.h
>> +++ b/include/hw/ppc/spapr_vio.h
>> @@ -73,6 +73,7 @@ struct VIOsPAPRDevice {
>>   struct VIOsPAPRBus {
>>       BusState bus;
>>       uint32_t next_reg;
>> +    uint32_t next_vty_reg;
>>       int (*init)(VIOsPAPRDevice *dev);
>>       int (*devnode)(VIOsPAPRDevice *dev, void *fdt, int node_off);
>>   };
> 


-- 
Alexey