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From: Cornelia Huck <cohuck@redhat.com>
To: Eric Farman <farman@linux.ibm.com>
Cc: Matthew Rosato <mjrosato@linux.ibm.com>,
	Halil Pasic <pasic@linux.ibm.com>,
	Jared Rossi <jrossi@linux.ibm.com>,
	linux-s390@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH v6 3/3] vfio-ccw: Serialize FSM IDLE state with I/O completion
Date: Wed, 12 May 2021 12:49:06 +0200	[thread overview]
Message-ID: <20210512124906.709d562c.cohuck@redhat.com> (raw)
In-Reply-To: <20210511195631.3995081-4-farman@linux.ibm.com>

On Tue, 11 May 2021 21:56:31 +0200
Eric Farman <farman@linux.ibm.com> wrote:

> Today, the stacked call to vfio_ccw_sch_io_todo() does three things:
>   1) Update a solicited IRB with CP information, and release the CP
>      if the interrupt was the end of a START operation.
>   2) Copy the IRB data into the io_region, under the protection of
>      the io_mutex
>   3) Reset the vfio-ccw FSM state to IDLE to acknowledge that
>      vfio-ccw can accept more work.
> The trouble is that step 3 is (A) invoked for both solicited and
> unsolicited interrupts, and (B) sitting after the mutex for step 2.
> This second piece becomes a problem if it processes an interrupt
> for a CLEAR SUBCHANNEL while another thread initiates a START,
> thus allowing the CP and FSM states to get out of sync. That is:
>     CPU 1                           CPU 2
>     fsm_do_clear()
>     fsm_irq()
>                                     fsm_io_request()
>     vfio_ccw_sch_io_todo()
>                                     fsm_io_helper()
> Since the FSM state and CP should be kept in sync, let's make a
> note when the CP is released, and rely on that as an indication
> that the FSM should also be reset at the end of this routine and
> open up the device for more work.
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
>  drivers/s390/cio/vfio_ccw_drv.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)

Looking good :)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>

  parent reply	other threads:[~2021-05-12 10:49 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-11 19:56 [PATCH v6 0/3] vfio-ccw: Fix interrupt handling for HALT/CLEAR Eric Farman
2021-05-11 19:56 ` [PATCH v6 1/3] vfio-ccw: Check initialized flag in cp_init() Eric Farman
2021-05-11 20:10   ` Matthew Rosato
2021-05-11 19:56 ` [PATCH v6 2/3] vfio-ccw: Reset FSM state to IDLE inside FSM Eric Farman
2021-05-11 20:38   ` Matthew Rosato
2021-05-11 19:56 ` [PATCH v6 3/3] vfio-ccw: Serialize FSM IDLE state with I/O completion Eric Farman
2021-05-11 20:45   ` Matthew Rosato
2021-05-12 10:49   ` Cornelia Huck [this message]
2021-05-13  1:05 ` [PATCH v6 0/3] vfio-ccw: Fix interrupt handling for HALT/CLEAR Halil Pasic
2021-05-13 18:33   ` Eric Farman
2021-05-14  0:29     ` Halil Pasic
2021-05-18  9:49 ` Cornelia Huck

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