From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pierre Morel Subject: Re: [PATCH 04/10] vfio: ccw: replace IO_REQ event with SSCH_REQ event Date: Wed, 23 May 2018 10:19:18 +0200 Message-ID: <3746e8a0-415f-3ba7-d7dc-be7835adc42f@linux.ibm.com> References: <1524149293-12658-1-git-send-email-pmorel@linux.vnet.ibm.com> <1524149293-12658-5-git-send-email-pmorel@linux.vnet.ibm.com> <20180425104138.1337aff5.cohuck@redhat.com> <24f638e4-2f7e-00e1-1efb-ff3fe524bca0@linux.vnet.ibm.com> <20180430173028.0dca976c.cohuck@redhat.com> <3c5a0677-4ed2-9bde-e6d8-d02ab69e0c2c@linux.vnet.ibm.com> <20180522173831.08f3b481.cohuck@redhat.com> Reply-To: pmorel@linux.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20180522173831.08f3b481.cohuck@redhat.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Cornelia Huck , Pierre Morel Cc: pasic@linux.vnet.ibm.com, bjsdjshi@linux.vnet.ibm.com, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org List-ID: On 22/05/2018 17:38, Cornelia Huck wrote: > [still backlog processing...] > > On Thu, 3 May 2018 14:06:51 +0200 > Pierre Morel wrote: > >> On 30/04/2018 17:30, Cornelia Huck wrote: >>> On Wed, 25 Apr 2018 15:52:19 +0200 >>> Pierre Morel wrote: >>> >>>> On 25/04/2018 10:41, Cornelia Huck wrote: >>>>> On Thu, 19 Apr 2018 16:48:07 +0200 >>>>> Pierre Morel wrote: >>>>>> diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h >>>>>> index 3284e64..93aab87 100644 >>>>>> --- a/drivers/s390/cio/vfio_ccw_private.h >>>>>> +++ b/drivers/s390/cio/vfio_ccw_private.h >>>>>> @@ -76,7 +76,7 @@ enum vfio_ccw_state { >>>>>> */ >>>>>> enum vfio_ccw_event { >>>>>> VFIO_CCW_EVENT_NOT_OPER, >>>>>> - VFIO_CCW_EVENT_IO_REQ, >>>>>> + VFIO_CCW_EVENT_SSCH_REQ, >>>>>> VFIO_CCW_EVENT_INTERRUPT, >>>>>> VFIO_CCW_EVENT_SCH_EVENT, >>>>>> /* last element! */ >>>>> I don't think we should separate the ssch handling. The major >>>>> difference to halt/clear is that it needs channel program translation. >>>>> Everything else (issuing the instruction and processing the interrupt) >>>>> are basically the same. If we just throw everything at the hardware >>>>> and let the host's channel subsystem figure it out, we already should >>>>> be fine with regard to most of the races. >>>> We must test at a moment or another the kind of request we do, >>>> cancel, halt and clear only need the subchannel id in register 1 and as >>>> you said are much more direct to implement. >>>> >>>> If we do not separate them here, we need a switch in the "do_io_request" >>>> function. >>>> Is it what you mean? >>> Yes. Most of the handling should be the same for any function. >> I really don't know, the 4 functions are quite different. >> >> - SSCH uses an ORB, and has a quite long kernel execution time for VFIO >> - there is a race between SSCH and the others instructions >> - XSCH makes subchannel no longer start pending, also reset the busy >> indications >> - CSCH cancels both SSCH and HSCH instruction, and perform path management >> - HSCH has different busy (entry) conditions > Roughly speaking, we have two categories: An asynchronous function is > performed (SSCH, HSCH, CSCH) or not (XSCH). So I would split out XSCH > in any case. > > SSCH, HSCH, CSCH all perform path management. I see them as kind of > escalating (i.e. CSCH 'beats' HSCH which 'beats' SSCH). I think they > are all similar enough, though, as we can call through to the real > hardware and have it sorted out there. > > Looking through the channel I/O instructions: > - RSCH should be handled with SSCH (as a special case). > - MSCH should also be handled in the long run, STSCH as well. > - SCHM is interesting, as it's not per-subchannel. We have some basic > handling of the instruction in QEMU, but it only emulates some ssch > counters and completely lacks support for the other fields. > - IIRC, there's also a CHSC command dealing with channel monitoring. We > currently fence off any CHSC that is not needed for Linux to run, but > there are some that might be useful for the guest (path handling > etc.) Hard to come to a conclusion here without access to the > documentation. > - I don't think we need to care about TSCH (other than keeping the > schib up to date, which we also need to do for STSCH). > - Likewise, TPI should be handled via emulation. > > Coming back to the original issue, I think we can easily handle SSCH > (and RSCH), HSCH and CSCH together (with the actual hardware doing the > heavy lifting anyway). For other instructions, we need separate > states/processing. > OK, I make the next version with this in mind. Thanks Pierre -- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany