Date:   Tue, 5 Jun 2018 16:10:52 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Pierre Morel <pmorel@...ux.vnet.ibm.com>
Cc:     pasic@...ux.vnet.ibm.com, bjsdjshi@...ux.vnet.ibm.com,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v2 08/10] vfio: ccw: Handling reset and shutdown with
 states

On 05/06/2018 14:18, Cornelia Huck wrote:
> On Fri, 25 May 2018 12:21:16 +0200
> Pierre Morel <pmorel@...ux.vnet.ibm.com> wrote:
>
>> Two new events, VFIO_CCW_EVENT_ONLINE and VFIO_CCW_EVENT_OFFLINE
>> allow to handle the enabling and disabling of a Sub Channel and
>> the init, shutdown, quiesce and reset operations are changed
>> accordingly.
>>
>> Signed-off-by: Pierre Morel <pmorel@...ux.vnet.ibm.com>
>> ---
>>   drivers/s390/cio/vfio_ccw_drv.c     | 44 ++++------------------
>>   drivers/s390/cio/vfio_ccw_fsm.c     | 75 +++++++++++++++++++++++++++++++++----
>>   drivers/s390/cio/vfio_ccw_ops.c     | 15 ++------
>>   drivers/s390/cio/vfio_ccw_private.h |  3 ++
>>   4 files changed, 82 insertions(+), 55 deletions(-)
>>
>> diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
>> index 6fc7668..3e7b514 100644
>> --- a/drivers/s390/cio/vfio_ccw_drv.c
>> +++ b/drivers/s390/cio/vfio_ccw_drv.c
>> @@ -30,41 +30,13 @@ int vfio_ccw_sch_quiesce(struct subchannel *sch)
>>   {
>>   	struct vfio_ccw_private *private = dev_get_drvdata(&sch->dev);
>>   	DECLARE_COMPLETION_ONSTACK(completion);

ooops, I have to pay more attention on the completions.
Same error that reported Heiko in patch 10/10.


>> -	int iretry, ret = 0;
>> -
>> -	spin_lock_irq(sch->lock);
>> -	if (!sch->schib.pmcw.ena)
>> -		goto out_unlock;
>> -	ret = cio_disable_subchannel(sch);
>> -	if (ret != -EBUSY)
>> -		goto out_unlock;
>> -
>> -	do {
>> -		iretry = 255;
>> -
>> -		ret = cio_cancel_halt_clear(sch, &iretry);
>> -		while (ret == -EBUSY) {
>> -			/*
>> -			 * Flush all I/O and wait for
>> -			 * cancel/halt/clear completion.
>> -			 */
>> -			private->completion = &completion;
>> -			spin_unlock_irq(sch->lock);
>> -
>> -			wait_for_completion_timeout(&completion, 3*HZ);
>> -
>> -			spin_lock_irq(sch->lock);
>> -			private->completion = NULL;
>> -			flush_workqueue(vfio_ccw_work_q);
>> -			ret = cio_cancel_halt_clear(sch, &iretry);understood
>> -		};
>> -
>> -		ret = cio_disable_subchannel(sch);
>> -	} while (ret == -EBUSY);
>> -out_unlock:
>> -	private->state = VFIO_CCW_STATE_NOT_OPER;
>> -	spin_unlock_irq(sch->lock);
>> -	return ret;
>> +
>> +	private->completion = &completion;
>> +	vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_OFFLINE);
>> +	wait_for_completion_interruptible_timeout(&completion, jiffies + 3*HZ);
>> +	if (private->state != VFIO_CCW_STATE_STANDBY)
>> +		return -EFAULT;
> -EFAULT really looks like the wrong error here. -EIO?

OK

>
> (I'm not sold on the whole concept here, though. See below.)
>
>> +	return 0;
>>   }
>>   
>>   static void vfio_ccw_sch_io_todo(struct work_struct *work)
>> @@ -95,8 +67,6 @@ static void vfio_ccw_sch_irq(struct subchannel *sch)
>>   	memcpy(&private->irb, irb, sizeof(*irb));
>>   
>>   	queue_work(vfio_ccw_work_q, &private->io_work);
>> -	if (private->completion)
>> -		complete(private->completion);
>>   }
>>   
>>   static int vfio_ccw_sch_probe(struct subchannel *sch)
>> diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c
>> index 20b909c..0acab2f 100644
>> --- a/drivers/s390/cio/vfio_ccw_fsm.c
>> +++ b/drivers/s390/cio/vfio_ccw_fsm.c
>> @@ -73,6 +73,53 @@ static int fsm_notoper(struct vfio_ccw_private *private)
>>   	return VFIO_CCW_STATE_NOT_OPER;
>>   }
>>   
>> +static int fsm_online(struct vfio_ccw_private *private)
>> +{
>> +	struct subchannel *sch = private->sch;
>> +	int ret = VFIO_CCW_STATE_IDLE;
>> +
>> +	spin_lock_irq(sch->lock);
>> +	if (cio_enable_subchannel(sch, (u32)(unsigned long)sch))
>> +		ret = VFIO_CCW_STATE_NOT_OPER;
>> +	spin_unlock_irq(sch->lock);
>> +
>> +	return ret;
>> +}
>> +static int fsm_offline(struct vfio_ccw_private *private)
>> +{
>> +	struct subchannel *sch = private->sch;
>> +	int ret = VFIO_CCW_STATE_STANDBY;
>> +
>> +	spin_lock_irq(sch->lock);
>> +	if (cio_disable_subchannel(sch))
>> +		ret = VFIO_CCW_STATE_NOT_OPER;
> So, what about a subchannel that is busy? Why should it go to the not
> oper state?

right, thanks.

>
> (And you should try to flush pending I/O and then try again in that
> case. Otherwise, you may have a still-enabled subchannel which may
> throw an interrupt.)

What about letting the guest doing this.
After giving him the right information on what happened of course.

>
>> +	spin_unlock_irq(sch->lock);
>> +	if (private->completion)
>> +		complete(private->completion);
>> +
>> +	return ret;
>> +}
>> +static int fsm_quiescing(struct vfio_ccw_private *private)
>> +{
>> +	struct subchannel *sch = private->sch;
>> +	int ret = VFIO_CCW_STATE_STANDBY;
>> +	int iretry = 255;
>> +
>> +	spin_lock_irq(sch->lock);
>> +	ret = cio_cancel_halt_clear(sch, &iretry);
>> +	if (ret == -EBUSY)
>> +		ret = VFIO_CCW_STATE_QUIESCING;
>> +	else if (private->completion)
>> +		complete(private->completion);
>> +	spin_unlock_irq(sch->lock);
>> +	return ret;
> If I read this correctly, you're calling cio_cancel_halt_clear() only
> once. What happened to the retry loop?

Same as above, what about letting the guest doing this?
And there are already 255 retries as part of the interface to cio.

>
>> +}
>> +static int fsm_quiescing_done(struct vfio_ccw_private *private)
>> +{
>> +	if (private->completion)
>> +		complete(private->completion);
>> +	return VFIO_CCW_STATE_STANDBY;
>> +}
>>   /*
>>    * No operation action.
>>    */
>> @@ -178,15 +225,10 @@ static int fsm_sch_event(struct vfio_ccw_private *private)
>>   static int fsm_init(struct vfio_ccw_private *private)
>>   {
>>   	struct subchannel *sch = private->sch;
>> -	int ret = VFIO_CCW_STATE_STANDBY;
>>   
>> -	spin_lock_irq(sch->lock);
>>   	sch->isc = VFIO_CCW_ISC;
>> -	if (cio_enable_subchannel(sch, (u32)(unsigned long)sch))
>> -		ret = VFIO_CCW_STATE_NOT_OPER;
>> -	spin_unlock_irq(sch->lock);
>>   
>> -	return ret;
>> +	return VFIO_CCW_STATE_STANDBY;
> Doesn't that change the semantic of the standby state?

It changes the FSM: NOT_OPER and STANDBY are clearly different.
Part of the initialization is now done in when putting the device online.


>
>>   }
>>   
>>   
>> @@ -196,6 +238,8 @@ static int fsm_init(struct vfio_ccw_private *private)
>>   fsm_func_t *vfio_ccw_jumptable[NR_VFIO_CCW_STATES][NR_VFIO_CCW_EVENTS] = {
>>   	[VFIO_CCW_STATE_NOT_OPER] = {
>>   		[VFIO_CCW_EVENT_INIT]		= fsm_init,
>> +		[VFIO_CCW_EVENT_ONLINE]		= fsm_nop,
>> +		[VFIO_CCW_EVENT_OFFLINE]	= fsm_nop,
>>   		[VFIO_CCW_EVENT_NOT_OPER]	= fsm_nop,
>>   		[VFIO_CCW_EVENT_SSCH_REQ]	= fsm_nop,
>>   		[VFIO_CCW_EVENT_INTERRUPT]	= fsm_nop,
>> @@ -203,13 +247,17 @@ fsm_func_t *vfio_ccw_jumptable[NR_VFIO_CCW_STATES][NR_VFIO_CCW_EVENTS] = {
>>   	},
>>   	[VFIO_CCW_STATE_STANDBY] = {
>>   		[VFIO_CCW_EVENT_INIT]		= fsm_nop,
>> +		[VFIO_CCW_EVENT_ONLINE]		= fsm_online,
>> +		[VFIO_CCW_EVENT_OFFLINE]	= fsm_offline,
>>   		[VFIO_CCW_EVENT_NOT_OPER]	= fsm_notoper,
>>   		[VFIO_CCW_EVENT_SSCH_REQ]	= fsm_io_error,
>> -		[VFIO_CCW_EVENT_INTERRUPT]	= fsm_irq,
>> +		[VFIO_CCW_EVENT_INTERRUPT]	= fsm_disabled_irq,
>>   		[VFIO_CCW_EVENT_SCHIB_CHANGED]	= fsm_sch_event,
>>   	},
>>   	[VFIO_CCW_STATE_IDLE] = {
>>   		[VFIO_CCW_EVENT_INIT]		= fsm_nop,
>> +		[VFIO_CCW_EVENT_ONLINE]		= fsm_nop,
>> +		[VFIO_CCW_EVENT_OFFLINE]	= fsm_offline,
>>   		[VFIO_CCW_EVENT_NOT_OPER]	= fsm_notoper,
>>   		[VFIO_CCW_EVENT_SSCH_REQ]	= fsm_io_request,
>>   		[VFIO_CCW_EVENT_INTERRUPT]	= fsm_irq,
>> @@ -217,6 +265,8 @@ fsm_func_t *vfio_ccw_jumptable[NR_VFIO_CCW_STATES][NR_VFIO_CCW_EVENTS] = {
>>   	},
>>   	[VFIO_CCW_STATE_BOXED] = {
>>   		[VFIO_CCW_EVENT_INIT]		= fsm_nop,
>> +		[VFIO_CCW_EVENT_ONLINE]		= fsm_nop,
>> +		[VFIO_CCW_EVENT_OFFLINE]	= fsm_quiescing,
>>   		[VFIO_CCW_EVENT_NOT_OPER]	= fsm_notoper,
>>   		[VFIO_CCW_EVENT_SSCH_REQ]	= fsm_io_busy,
>>   		[VFIO_CCW_EVENT_INTERRUPT]	= fsm_irq,
>> @@ -224,9 +274,20 @@ fsm_func_t *vfio_ccw_jumptable[NR_VFIO_CCW_STATES][NR_VFIO_CCW_EVENTS] = {
>>   	},
>>   	[VFIO_CCW_STATE_BUSY] = {
>>   		[VFIO_CCW_EVENT_INIT]		= fsm_nop,
>> +		[VFIO_CCW_EVENT_ONLINE]		= fsm_nop,
>> +		[VFIO_CCW_EVENT_OFFLINE]	= fsm_quiescing,
>>   		[VFIO_CCW_EVENT_NOT_OPER]	= fsm_notoper,
>>   		[VFIO_CCW_EVENT_SSCH_REQ]	= fsm_io_busy,
>>   		[VFIO_CCW_EVENT_INTERRUPT]	= fsm_irq,
>>   		[VFIO_CCW_EVENT_SCHIB_CHANGED]	= fsm_sch_event,
>>   	},
>> +	[VFIO_CCW_STATE_QUIESCING] = {
>> +		[VFIO_CCW_EVENT_INIT]		= fsm_nop,
>> +		[VFIO_CCW_EVENT_ONLINE]		= fsm_nop,
>> +		[VFIO_CCW_EVENT_OFFLINE]	= fsm_nop,
>> +		[VFIO_CCW_EVENT_NOT_OPER]	= fsm_notoper,
>> +		[VFIO_CCW_EVENT_SSCH_REQ]	= fsm_io_busy,
>> +		[VFIO_CCW_EVENT_INTERRUPT]	= fsm_quiescing_done,
>> +		[VFIO_CCW_EVENT_SCHIB_CHANGED]	= fsm_sch_event,
>> +	},
> Your idea here seems to be to go to either disabling the subchannel
> directly or flushing out I/O first, depending on the state you're in.
> The problem is that you may need retries in any case (the subchannel
> may be status pending if it is enabled; not necessarily by any I/O that
> had been started, but also from an unsolicited notification.)

I wanted to let the guest do the retries as he wants to.
Somehow we must give the right response back to the guest
and take care of the error number we give back.

I will get a better look at this.

>
>>   };
>> diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
>> index ea8fd64..b202e73 100644
>> --- a/drivers/s390/cio/vfio_ccw_ops.c
>> +++ b/drivers/s390/cio/vfio_ccw_ops.c
>> @@ -21,21 +21,14 @@ static int vfio_ccw_mdev_reset(struct mdev_device *mdev)
>>   
>>   	private = dev_get_drvdata(mdev_parent_dev(mdev));
>>   	sch = private->sch;
>> -	/*
>> -	 * TODO:
>> -	 * In the cureent stage, some things like "no I/O running" and "no
>> -	 * interrupt pending" are clear, but we are not sure what other state
>> -	 * we need to care about.
>> -	 * There are still a lot more instructions need to be handled. We
>> -	 * should come back here later.
>> -	 */
> This is still true, no? I'm thinking about things like channel monitors
> and the like (even if we don't support them yet).

I think that this is not the place to put this remark since here
we should send an event to the FSM, having new states
will be handled as FSM states.
I put it back, here or where I think it belong if I find another
place after resolving the RESET problem.

>
>> +
>>   	ret = vfio_ccw_sch_quiesce(sch);
>>   	if (ret)
>>   		return ret;
>> +	vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_ONLINE);
>>   
>> -	ret = cio_enable_subchannel(sch, (u32)(unsigned long)sch);
>> -	if (!ret)
>> -		private->state = VFIO_CCW_STATE_IDLE;
>> +	if (!(private->state == VFIO_CCW_STATE_IDLE))
>> +		ret = -EFAULT;
> The -EFAULT looks wrong here as well.

yes

>
> I'm also not sure whether we should conflate enabling/disabling a
> device and doing a reset.

I fully agree, just did not change the existing.

>
>>   
>>   	return ret;
>>   }
>> diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h
>> index c5455a9..ad59091 100644
>> --- a/drivers/s390/cio/vfio_ccw_private.h
>> +++ b/drivers/s390/cio/vfio_ccw_private.h
>> @@ -68,6 +68,7 @@ enum vfio_ccw_state {
>>   	VFIO_CCW_STATE_IDLE,
>>   	VFIO_CCW_STATE_BOXED,
>>   	VFIO_CCW_STATE_BUSY,
>> +	VFIO_CCW_STATE_QUIESCING,
>>   	/* last element! */
>>   	NR_VFIO_CCW_STATES
>>   };
>> @@ -81,6 +82,8 @@ enum vfio_ccw_event {
>>   	VFIO_CCW_EVENT_SSCH_REQ,
>>   	VFIO_CCW_EVENT_INTERRUPT,
>>   	VFIO_CCW_EVENT_SCHIB_CHANGED,
>> +	VFIO_CCW_EVENT_ONLINE,
>> +	VFIO_CCW_EVENT_OFFLINE,
>>   	/* last element! */
>>   	NR_VFIO_CCW_EVENTS
>>   };

Thanks a lot for the review.

I will address all the remarks in the next version.

Thanks,

Pierre


-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany

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