Re: [PATCH kvm-unit-tests v1 6/6] lib: s390x: smp: Convert remaining smp_sigp to _retry

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

On Fri, 2022-03-04 at 11:56 +0100, Janosch Frank wrote:
> On 3/3/22 22:04, Eric Farman wrote:
> > A SIGP SENSE is used to determine if a CPU is stopped or operating,
> > and thus has a vested interest in ensuring it received a CC0 or
> > CC1,
> > instead of a CC2 (BUSY). But, any order could receive a CC2
> > response,
> > and is probably ill-equipped to respond to it.
> 
> sigp sense running status doesn't return a cc2, only sigp sense does
> afaik.

The KVM routine handle_sigp_dst() returns the CC2 if a STOP/RESTART IRQ
is pending for any non-reset order, before it gets to the switch
statement that would route to the SIGP SENSE RUNNING handler.

> Looking at the KVM implementation tells me that it's not doing more
> than 
> looking at the R bit in the sblk.
> 
> > In practice, the order is likely to only encounter this when racing
> > with a SIGP STOP (AND STORE STATUS) or SIGP RESTART order, which
> > are
> > unlikely. But, since it's not impossible, let's convert the library
> > calls that issue a SIGP to loop on CC2 so the callers do not need
> > to react to that possible outcome.
> > 
> > Signed-off-by: Eric Farman <farman@linux.ibm.com>
> > ---
> >   lib/s390x/smp.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
> > index 85b046a5..2e476264 100644
> > --- a/lib/s390x/smp.c
> > +++ b/lib/s390x/smp.c
> > @@ -85,7 +85,7 @@ bool smp_cpu_stopped(uint16_t idx)
> >   
> >   bool smp_sense_running_status(uint16_t idx)
> >   {
> > -	if (smp_sigp(idx, SIGP_SENSE_RUNNING, 0, NULL) !=
> > SIGP_CC_STATUS_STORED)
> > +	if (smp_sigp_retry(idx, SIGP_SENSE_RUNNING, 0, NULL) !=
> > SIGP_CC_STATUS_STORED)
> >   		return true;
> >   	/* Status stored condition code is equivalent to cpu not
> > running. */
> >   	return false;
> > @@ -169,7 +169,7 @@ static int smp_cpu_restart_nolock(uint16_t idx,
> > struct psw *psw)
> >   	 * running after the restart.
> >   	 */
> >   	smp_cpu_stop_nolock(idx, false);
> > -	rc = smp_sigp(idx, SIGP_RESTART, 0, NULL);
> > +	rc = smp_sigp_retry(idx, SIGP_RESTART, 0, NULL);
> >   	if (rc)
> >   		return rc;
> >   	/*