Re: [PATCH v1 4/4] s390x: Testing the Subchannel I/O read

Pierre Morel
2019-11-22T09:03:28Z

On 2019-11-21 17:02, Cornelia Huck wrote:
> On Thu, 14 Nov 2019 11:11:18 +0100
> Pierre Morel <pmorel@linux.ibm.com> wrote:
>
>> On 2019-11-13 14:05, Cornelia Huck wrote:
>>> On Wed, 13 Nov 2019 13:23:19 +0100
>>> Pierre Morel <pmorel@linux.ibm.com> wrote:
>>>
>>>> This simple test test the I/O reading by the SUB Channel by:
>>>> - initializing the Channel SubSystem with predefined CSSID:
>>>> 0xfe000000 CSSID for a Virtual CCW
>>> 0 should be fine with recent QEMU versions as well, I guess?
>> Right
>>
>>
>>>
>>>> 0x00090000 SSID for CCW-PONG
>>> subchannel id, or subchannel set id?
>> hum, only part of, I had SSID (Subchannel Set ID) 4 (a.k.a m bit) + Bit
>> 47  =1
>>
>> But as you said, I can use CSSID 0 and m = 0 which makes:
>>
>> Subsystem Identification word = 0x00010000
> Yeah, I was mainly confused by the name 'SSID'.

Hum, yes sorry, I posted this to give a response to the kvm-test-unit
css test.

I should have a lot more rework this old device before to post this series.
In between I did, so I will post a v2 which will suppress all these
approximations.

>
>>>> - initializing the ORB pointing to a single READ CCW
>>> Out of curiosity: Would using a NOP also be an option?
>> It will work but will not be handled by this device, css.c intercept it
>> in sch_handle_start_func_virtual.
>>
>> AFAIU If we want to have a really good testing environment, for driver
>> testing for exemple, then it would be interesting to add a new
>> do_subchannel_work callback like do_subchannel_work_emulation along with
>> the _virtual and _paththrough variantes.
>>
>> Having a dedicated callback for emulation, we can answer to any CSS
>> instructions and SSCH commands, including NOP and TIC.
> I guess that depends on what you want to test; if you actually want to
> test device emulation as used by virtio etc., you obviously want to go
> through the existing _virtual callback :)

The first goal is to test basic I/O from inside the kvm-unit-test,
producing errors and see how the system respond to errors.

In a standard system errors will be generated by QEMU analysing the I/O
instruction after interception.

In a secured guest, we expect the same errors, however we want to check
this.

This PONG device is intended to be low level, no VIRTIO, and to allow
basic I/O.

>
> The actual motivation behind my question was:
> Is it possible to e.g. throw NOP (or TIC, or something else not
> device-specific) at a normal, existing virtio device for test purposes?
> You'd end up testing the common emulation code without needing any
> extra support in QEMU. No idea how useful that would be.

Writing a VIRTIO driver inside the kvm-unit-test is something we can do
in the future.

As you said, the common code already handle NOP and TIC, the
interpretation of the
CCW chain, once the SSCH has been intercepted is done by QEMU.
I do not think it would be different with SE.

>
>> My goal here was to quickly develop a device answering to some basic
>> READ/WRITE command to start memory transfers from inside a guest without
>> Linux and without implementing VIRTIO in KVM tests.
> Yes, if you want to do some simple memory transfers, virtio is probably
> not the first choice. Would e.g. doing a SenseID or so actually be
> useful in some way already? After all, it does transfer memory (but
> only in one direction).

The kvm-unit-test part is in development too.

Doing a SenseID will be implemented to recognize the PONG device.

>
>>>> +static inline int rsch(unsigned long schid)
>>> I don't think anyone has tried rsch with QEMU before; sounds like a
>>> good idea to test this :)
>> With an do_subchannel_work_emulation() callback?
> You probably need to build a simple channel program that suspends
> itself and can be resumed later.

Yes, that is something I plan to do.

To sum-up:

in kvm-unit-test: implement all I/O instructions and force instructions
errors, like memory error, operand etc. and expect the right reaction of
the system.

in QEMU, add the necessary infrastructure to test this.

Regards,

Pierre

--
Pierre Morel
IBM Lab Boeblingen