From: Cornelia Huck <cohuck@redhat.com>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: Jared Rossi <jrossi@linux.ibm.com>,
Eric Farman <farman@linux.ibm.com>,
linux-s390@vger.kernel.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] vfio-ccw: Enable transparent CCW IPL from DASD
Date: Thu, 23 Apr 2020 17:11:03 +0200 [thread overview]
Message-ID: <20200423171103.497dcd02.cohuck@redhat.com> (raw)
In-Reply-To: <20200423155620.493cb7cb.pasic@linux.ibm.com>
On Thu, 23 Apr 2020 15:56:20 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:
> On Fri, 17 Apr 2020 14:29:39 -0400
> Jared Rossi <jrossi@linux.ibm.com> wrote:
>
> > Remove the explicit prefetch check when using vfio-ccw devices.
> > This check is not needed as all Linux channel programs are intended
> > to use prefetch and will be executed in the same way regardless.
>
> Hm. This is a guest thing or? So you basically say, it is OK to do
> this, because you know that the guest is gonna be Linux and that it
> the channel program is intended to use prefetch -- but the ORB supplied
> by the guest that designates the channel program happens to state the
> opposite.
>
> Or am I missing something?
I see this as a kind of architecture compliance/ease of administration
tradeoff, as we none of the guests we currently support uses something
that breaks with prefetching outside of IPL (which has a different
workaround).
One thing that still concerns me a bit is debuggability if a future
guest indeed does want to dynamically rewrite a channel program: the
guest thinks it instructed the device to not prefetch, and then
suddenly things do not work as expected. We can log when a guest
submits an orb without prefetch set, but we can't find out if the guest
actually does something that relies on non-prefetch.
The only correct way to handle this would be to actually implement
non-prefetch processing, where I would not really know where to even
start -- and then we'd only have synthetic test cases, for now. None of
the options are pleasant :(
next prev parent reply other threads:[~2020-04-23 15:11 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-17 18:29 [PATCH 0/1] vfio-ccw: Enable transparent CCW IPL from DASD Jared Rossi
2020-04-17 18:29 ` [PATCH 1/1] " Jared Rossi
2020-04-20 12:13 ` Cornelia Huck
2020-04-24 13:02 ` Halil Pasic
2020-04-23 13:56 ` Halil Pasic
2020-04-23 15:11 ` Cornelia Huck [this message]
2020-04-23 20:25 ` Eric Farman
2020-04-24 12:50 ` Halil Pasic
2020-04-29 0:38 ` Jared Rossi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200423171103.497dcd02.cohuck@redhat.com \
--to=cohuck@redhat.com \
--cc=farman@linux.ibm.com \
--cc=jrossi@linux.ibm.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=pasic@linux.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).