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

[Eric Farman <farman@linux.ibm.com>]

On 5/6/19 11:37 AM, Cornelia Huck wrote:
> On Fri,  3 May 2019 15:49:12 +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),
> 
> The "Common I/O Device Commands" document actually defines this :)

Blech, okay so I didn't look early enough in that document.  Section 1.5 
it is.  :)

> 
>> 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.
> 
> But I agree that everything possible should be sent 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(-)
>>
>> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
>> index 36d76b821209..c0a52025bf06 100644
>> --- a/drivers/s390/cio/vfio_ccw_cp.c
>> +++ b/drivers/s390/cio/vfio_ccw_cp.c
>> @@ -289,8 +289,6 @@ static long copy_ccw_from_iova(struct channel_program *cp,
>>   #define ccw_is_read_backward(_ccw) (((_ccw)->cmd_code & 0x0F) == 0x0C)
>>   #define ccw_is_sense(_ccw) (((_ccw)->cmd_code & 0x0F) == CCW_CMD_BASIC_SENSE)
>>   
>> -#define ccw_is_test(_ccw) (((_ccw)->cmd_code & 0x0F) == 0)
>> -
>>   #define ccw_is_noop(_ccw) ((_ccw)->cmd_code == CCW_CMD_NOOP)
>>   
>>   #define ccw_is_tic(_ccw) ((_ccw)->cmd_code == CCW_CMD_TIC)
>> @@ -314,6 +312,10 @@ static inline int ccw_does_data_transfer(struct ccw1 *ccw)
>>   	if (ccw->count == 0)
>>   		return 0;
>>   
>> +	/* If the command is a NOP, then no data will be transferred */
>> +	if (ccw_is_noop(ccw))
>> +		return 0;
>> +
> 
> Don't you need to return 0 here for any test command as well?
> 
> (If I read the doc correctly, we'll just get a unit check in any case,
> as there are no parallel I/O interfaces on modern s390 boxes. Even if
> we had a parallel I/O interface, we'd just collect the status, and not
> get any data transfer. FWIW, the QEMU ccw interpreter for emulated
> devices rejects test ccws with a channel program check, which looks
> wrong; should be a command reject instead.)

I will go back and look.  I thought when I sent a test command with an 
address that wasn't translated I got an unhappy result, which is why I 
ripped this check out.

I was trying to use test CCWs as a safety valve for Halil's Status 
Modifier concern, so maybe I had something else wrong on that pile. 
(The careful observer would note that that code was not included here.  :)

> 
>>   	/* If the skip flag is off, then data will be transferred */
>>   	if (!ccw_is_skip(ccw))
>>   		return 1;
>> @@ -398,7 +400,7 @@ static void ccwchain_cda_free(struct ccwchain *chain, int idx)
>>   {
>>   	struct ccw1 *ccw = chain->ch_ccw + idx;
>>   
>> -	if (ccw_is_test(ccw) || ccw_is_noop(ccw) || ccw_is_tic(ccw))
>> +	if (ccw_is_tic(ccw))
>>   		return;
>>   
>>   	kfree((void *)(u64)ccw->cda);
>> @@ -723,9 +725,6 @@ static int ccwchain_fetch_one(struct ccwchain *chain,
>>   {
>>   	struct ccw1 *ccw = chain->ch_ccw + idx;
>>   
>> -	if (ccw_is_test(ccw) || ccw_is_noop(ccw))
>> -		return 0;
>> -
>>   	if (ccw_is_tic(ccw))
>>   		return ccwchain_fetch_tic(chain, idx, cp);
>>   
>