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

[Eric Farman <farman@xxxxxxxxxxxxx>]

On 5/6/19 8:56 AM, Pierre Morel wrote:
> On 03/05/2019 15:49, Eric Farman 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.
> >
> > [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@xxxxxxxxxxxxx>
> > ---
> >   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;
> > +
> >       /* 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))
>
>
> AFAIR, we introduced this code to protect against noop and test with a 
> non zero CDA.
> This could go away only if there is somewhere the guaranty that noop 
> have always a null CDA (same for test).

What was generating either the null or "test" command codes?  I can 
provide plenty of examples for both these command codes and how they 
look coming out of vfio-ccw now.

The noop check is moved up into the "does data transfer" routine, to 
determine whether the pages should be pinned or not.  Regardless of 
whether or not the input CDA is null, we'll end up with a CCW pointing 
to a valid IDAL of invalid addresses.

The "test" command codes always struck me as funky, because x18 and xF8 
and everything in between that ends in x8 is architecturally invalid 
too, but we don't check for them like we do for things that end in x0. 
And there's a TON of other opcodes that are invalid for today's ECKD 
devices, or perhaps were valid for older DASD but have since been 
deprecated, or are only valid for non-DASD device types.  We have no 
logic to permit them, either.  If those CCWs had a non-zero CDA, we 
either pin it successfully and let the targeted device sort it out or an 
error occurs and we fail at that point.  (QEMU will see a "wirte" region 
error of -EINVAL because of vfio_pin_pages())

> >           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);