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Tue, 21 Apr 2020 08:29:42 +0000 (UTC) Received: from gondolin (ovpn-112-226.ams2.redhat.com [10.36.112.226]) by smtp.corp.redhat.com (Postfix) with ESMTP id 15E3C60C63; Tue, 21 Apr 2020 08:29:40 +0000 (UTC) Date: Tue, 21 Apr 2020 10:29:37 +0200 From: Cornelia Huck To: Jared Rossi Subject: Re: [PATCH 1/1] vfio-ccw: Enable transparent CCW IPL from DASD Message-ID: <20200421102937.511fde3a.cohuck@redhat.com> In-Reply-To: <2fe2e12dee1799afee088bed88e6c671@linux.vnet.ibm.com> References: <20200417183838.11796-1-jrossi@linux.ibm.com> <20200417183838.11796-2-jrossi@linux.ibm.com> <20200420142617.5e255265.cohuck@redhat.com> <20200420142917.206d36a5.cohuck@redhat.com> <2fe2e12dee1799afee088bed88e6c671@linux.vnet.ibm.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/21 01:28:51 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eric Farman , qemu-s390x@nongnu.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 20 Apr 2020 18:35:58 -0400 Jared Rossi wrote: > On 2020-04-20 08:29, Cornelia Huck wrote: > > On Mon, 20 Apr 2020 14:26:17 +0200 > > Cornelia Huck wrote: > > > >> On Fri, 17 Apr 2020 14:38:38 -0400 > >> Jared Rossi 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. > >> > >> As already commented on the Linux patch: Can we log something, so this > >> is debuggable if this statement does not hold true in the future? > >> > > Agreed. I will work on debugging improvements so that any future issues > related to unintended prefetching are more clearly logged. Great. > > >> > > >> > Signed-off-by: Jared Rossi > >> > --- > >> > hw/vfio/ccw.c | 13 +++---------- > >> > 1 file changed, 3 insertions(+), 10 deletions(-) > >> > > >> > diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c > >> > index 50cc2ec75c..e649377b68 100644 > >> > --- a/hw/vfio/ccw.c > >> > +++ b/hw/vfio/ccw.c > >> > @@ -74,16 +74,9 @@ static IOInstEnding vfio_ccw_handle_request(SubchDev *sch) > >> > struct ccw_io_region *region = vcdev->io_region; > >> > int ret; > >> > > >> > - if (!(sch->orb.ctrl0 & ORB_CTRL0_MASK_PFCH)) { > >> > - if (!(vcdev->force_orb_pfch)) { > >> > - warn_once_pfch(vcdev, sch, "requires PFCH flag set"); > >> > - sch_gen_unit_exception(sch); > >> > - css_inject_io_interrupt(sch); > >> > - return IOINST_CC_EXPECTED; > >> > - } else { > >> > - sch->orb.ctrl0 |= ORB_CTRL0_MASK_PFCH; > >> > - warn_once_pfch(vcdev, sch, "PFCH flag forced"); > >> > - } > >> > + if (!(sch->orb.ctrl0 & ORB_CTRL0_MASK_PFCH) && vcdev->force_orb_pfch) { > >> > + sch->orb.ctrl0 |= ORB_CTRL0_MASK_PFCH; > >> > + warn_once_pfch(vcdev, sch, "PFCH flag forced"); > >> > } > >> > >> What happens when you run it with an old kernel? I guess the I/O is > >> only rejected later (after a trip into the kernel), but has that path > >> ever been tested? > >> > > Yes, this was tested and you are correct that the kernel will reject the > I/O unless > the corresponding patch is also applied there. I will revisit this path > while I'm > updating the logging to ensure that any potential interactions are > appropriately > considered. I've looked at the code again and it seems that the kernel will end up signaling -EOPNOTSUPP to us on that case, which causes the same unit exception as without this patch, so we should be all good. > > >> > > >> > QEMU_BUILD_BUG_ON(sizeof(region->orb_area) != sizeof(ORB)); > >> > > > > Oh, and do we want to deprecate the force prefetch interface in the > > future? We probably need to wait a bit, until the kernel changes have > > become widely available. > > Yes, I think we will want to deprecate it at an appropriate time in the > future. >