Re: [PATCH v2 7/7] s390/cio: Remove vfio-ccw checks of command codes

Eric Farman
2019-05-15T13:40:37Z

On 5/15/19 8:43 AM, Cornelia Huck wrote:
> On Wed, 15 May 2019 01:42:48 +0200
> Eric Farman <farman@linux.ibm.com> wrote:
>
>> If the CCW being processed is a No-Operation, then by definition no
>> data is being transferred. Let's fold those checks into the normal
>> CCW processors, rather than skipping out early.
>>
>> Likewise, if the CCW being processed is a "test" (an invented
>> definition to simply mean it ends in a zero), let's permit that to go
>> through to the hardware. There's nothing inherently unique about
>> those command codes versus one that ends in an eight [1], or any other
>> otherwise valid command codes that are undefined for the device type
>> in question.
>
> Hm... let's tweak that a bit? It's not that "test" is an invented
> category; it's just that this has not been a valid command for
> post-s/370 and therefore should not get any special treatment and just
> be sent to the hardware?

Agreed, I should've re-read that one before I sent it... How about:

Likewise, if the CCW being processed is a "test" (a category defined
here as an opcode that contains zero in the lowest four bits) then no
special processing is necessary as far as vfio-ccw is concerned.
These command codes have not been valid since the S/370 days, meaning
they are invalid in the same way as one that ends in an eight [1] or
an otherwise valid command code that is undefined for the device type
in question. Considering that, let's just process "test" CCWs like
any other CCW, and send everything to the hardware.

>
>>
>> [1] POPS states that a x08 is a TIC CCW, and that having any high-order
>> bits enabled is invalid for format-1 CCWs. For format-0 CCWs, the
>> high-order bits are ignored.
>>
>> Signed-off-by: Eric Farman <farman@linux.ibm.com>
>> ---
>> drivers/s390/cio/vfio_ccw_cp.c | 11 +++++------
>> 1 file changed, 5 insertions(+), 6 deletions(-)
>