Re: [RFC PATCH] Disable Book-E KVM support?

[Christian Zigotzky <chzigotzky@xenosoft.de>]

Further information: 
https://lists.nongnu.org/archive/html/qemu-ppc/2022-12/msg00000.html

-- Christian


On 04 December 2022 at 12:33 pm, Christian Zigotzky wrote:
> Hi All,
>
> We regularly use QEMU with KVM HV on our A-EON AmigaOne X5000 machines 
> (book3e). It works fast and without any problems.
>
> Screenshot tour of QEMU/KVM HV on our AmigaOnes:
>
> - https://i.ibb.co/m4vgwNT/Kernel-6-1-rc3-Power-PC.png
> - https://i.ibb.co/Fwdjf7Z/Kernel-6-0-rc6-Power-PC.png
> - https://i.ibb.co/LYnJGdF/Kernel-5-19-rc5-Power-PC-2.png
> - https://i.ibb.co/vz1Wm5z/QEMU-with-9p-and-USB-sound.png
> - https://i.ibb.co/ScMjtp7/Kernel-5-17-alpha5-Power-PC.png
> - https://i.ibb.co/LQryFcK/Kernel-5-17-alpha4-Power-PC.png
> - https://i.ibb.co/kKLx9mf/Kernel-5-10-89-Power-PC.png
> - https://i.ibb.co/LRG1RDV/Kernel-5-10-89-Power-PC-2.png
> - https://i.ibb.co/NCFqY0k/QEMU-USB-Audio-on-Void-PPC.png
> - https://i.ibb.co/N1vL5Kd/Kernel-5-16-alpha3-Power-PC.png
> - https://i.ibb.co/SwjTyJk/Kernel-5-16-alpha1-Power-PC.png
> - https://i.ibb.co/LkpWNPx/Kernel-5-15-rc5-Power-PC.png
> - https://i.ibb.co/F8q1jDR/Kernel-5-15-rc4-Power-PC.png
> - https://i.ibb.co/zZxrbhV/Kernel-5-15-alpha6-Power-PC.png
> - 
> https://i.pinimg.com/originals/a8/8b/42/a88b422870201887fc01ef44ddc1a235.png
> - 
> https://i.pinimg.com/originals/57/d9/83/57d98324cd055b7ae00a87ad5a45a42f.png
> - 
> https://i.pinimg.com/originals/f2/a5/e3/f2a5e34e2015381b0cb87cc51232a8bc.png
> - 
> https://i.pinimg.com/originals/c5/0d/85/c50d85d7e8f20b4caa1a439faf751964.png
> - 
> https://i.pinimg.com/originals/6e/3b/59/6e3b59fe10276c5644b15622a81f43f1.png
>
> We solved some issues:
>
> - https://forum.hyperion-entertainment.com/viewtopic.php?p=54357#p54357
> - 
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2021-November/236307.html
> - 
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2022-September/249021.html
> - https://lists.ozlabs.org/pipermail/linuxppc-dev/2021-May/229103.html
> - 
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2021-January/223342.html
> - https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-August/216379.html
> - 
> https://forum.hyperion-entertainment.com/viewtopic.php?f=58&t=4655&p=53393&hilit=KVM#p53393
> - https://forum.hyperion-entertainment.com/viewtopic.php?p=53209#p53209
>
> Please, do not remove KVM support from Book3e because it works without 
> any problems and fast. We need it for our work.
>
> Thanks,
> Christian
>
>
>
>
>     On 12/2/22 12:04, Daniel Henrique Barboza wrote:
>
>         On 11/30/22 17:45, Crystal Wood wrote:
>
>             On Mon, 2022-11-28 at 14:36 +1000, Nicholas Piggin wrote:
>
>                 BookE KVM is in a deep maintenance state, I'm not sure 
> how much testing
>                 it gets. I don't have a test setup, and it does not 
> look like QEMU has
>                 any HV architecture enabled. It hasn't been too 
> painful but there are
>                 some cases where it causes a bit of problem not being 
> able to test, e.g.,
>
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2022-November/251452.html
>
>                 Time to begin removal process, or are there still 
> people using it? I'm
>                 happy to to keep making occasional patches to try keep 
> it going if
>                 there are people testing upstream. Getting HV support 
> into QEMU would
>                 help with long term support, not sure how big of a job 
> that would be.
>
>
>             Not sure what you mean about QEMU not having e500 HV 
> support?  I don't know if
>             it's bitrotted, but it's there.
>
>
>         AFAIK all QEMU ppc boards, aside from pSeries and the Mac 
> ones, are always used
>         in
>         emulated mode in an use case similar to what Bernhard 
> described in his reply
>         (run
>         in x86 due to lack of ppc hardware).
>
>         I am not aware of e500 KVM support in QEMU since I never 
> attempted it. But yes,
>         it is present, but poorly tested - if tested at all. And the 
> reason why there's
>         no push on our side to removed it from QEMU is because its 
> code is so entwined
>         with pSeries KVM that it would take too much effort.
>
>         Do not take the presence of e500 KVM support in QEMU as a 
> blocker to disabled
>         it in
>         the kernel. As far as the current QEMU usage goes e500 KVM can 
> be removed
>         without
>         too much drama from our side.
>
>         Cedric, do you have any opinions about it?
>
>
>
>     I can not tell how much e500 KVM is used. The last report we had
>     on the topic was :
>
> https://lore.kernel.org/all/R4OPHT$7F12C66D1107397991E0E4C978FE6AF1@locati.it/ 
>
>
>     and the last commit mentioning e500 VMs I could find is cb3778a045,
>     which brings us back to QEMU 2.2 or so.
>
>     It would be nice to 'quickly' check the state of the KVM stack on
>     such boards and, may be, plan for more cleanups.
>
>
>     Thanks,
>
>     C.
>
>
>
>         Daniel
>
>
>
>             I don't know whether anyone is still using this, but if 
> they are, it's
>             probably e500mc and not e500v2 (which involved a bunch of 
> hacks to get almost-
>             sorta-usable performance out of hardware not designed for 
> virtualization).  I
>             do see that there have been a few recent patches on QEMU 
> e500 (beyond the
>             treewide cleanup type stuff), though I don't know if 
> they're using KVM.  CCing
>             them and the QEMU list.
>
>             I have an e6500 I could occasionally test on, if it turns 
> out people do still
>             care about this.  Don't count me as the use case, though. :-)
>
>             FWIW, as far as the RECONCILE_IRQ_STATE issue, that used 
> to be done in
>             kvmppc_handle_exit(), but was moved in commit 9bd880a2c882 
> to be "cleaner and
>             faster". :-P
>
>             -Crystal
>
>
>
> Dear all,
> please, do not proceed removing KVM support to Book3e.
>
> The PowerProgressCommunity, our not-for-profit organisation of PowerPC 
> and alternative platforms enthusiasts is in the process of hardware 
> testing our new “Powerboard Tyche”, a fully open hardware motherboard 
> for a laptop based on a NXP T2080 which is a Book3e e6500 CPU (4 
> physical cores, 8 logical cores), see our recent blog post about it
> https://www.powerpc-notebook.org/2022/12/prototypes-produced-lets-go-on-hardware-tests/ 
>
>
> With such a board we hope to have a new small niche group of users of 
> a PowerPC Book3e platform that will be more than happy to keep using 
> QEMU with KVM enabled as using VMs without KVM is way too slow.
>
> At the moment we still have a working NXP DevKit based on the same 
> T2080 CPU and thank to a patch submitted back in December 2021 we can 
> use QEMU with KVM enable on it.
> The only issue we have so far is that it only starts when setting it 
> as “e5500” (that does not have altivec) because starting it with e6500 
> (that has altivec) it does not start.
>
> We published a blog post about QEMU with KVM enable back in December 
> 2021, I made a screenshot with multiple QEMU instances
> https://www.powerpc-notebook.org/2021/12/december-2021-updates-facing-electronic-components-shortages/ 
>
>
> I am also aware of users of the A-Eon AmigaOne X5000 computers (still 
> being produced and sold) that successfully use QEMU with KVM enabled, 
> their system are based either on a NXP P5020 or P5040, both Book3e 
> e5500, so without altivec.
>
> So, again, please, do not remove KVM support to Book3e we need that!
>
> Regards,
> Mario
>