linux-kernel - Re: [PATCH v4 1/1] vfio-ccw: Enable transparent CCW IPL from DASD

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Message-ID: <20200508124725.58fb985a.cohuck@redhat.com>
Date:   Fri, 8 May 2020 12:47:25 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Jared Rossi <jrossi@...ux.ibm.com>
Cc:     Eric Farman <farman@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/1] vfio-ccw: Enable transparent CCW IPL from DASD

On Wed,  6 May 2020 17:24:40 -0400
Jared Rossi <jrossi@...ux.ibm.com> wrote:

> Remove the explicit prefetch check when using vfio-ccw devices.
> This check does not trigger in practice as all Linux channel programs
> are intended to use prefetch.
> 
> It is expected that all ORBs issued by Linux will request prefetch.
> Although non-prefetching ORBs are not rejected, they will prefetch
> nonetheless. A warning is issued up to once per 5 seconds when a
> forced prefetch occurs.
> 
> A non-prefetch ORB does not necessarily result in an error, however
> frequent encounters with non-prefetch ORBs indicate that channel
> programs are being executed in a way that is inconsistent with what
> the guest is requesting. While there is currently no known case of an
> error caused by forced prefetch, it is possible in theory that forced
> prefetch could result in an error if applied to a channel program that
> is dependent on non-prefetch.
> 
> Signed-off-by: Jared Rossi <jrossi@...ux.ibm.com>
> ---
>  Documentation/s390/vfio-ccw.rst |  6 ++++++
>  drivers/s390/cio/vfio_ccw_cp.c  | 19 ++++++++++++-------
>  2 files changed, 18 insertions(+), 7 deletions(-)
> 

Thanks, applied.