Re: [PATCH 0/15] KVM: MIPS: Add Loongson-3 support (Host Side)

[Huacai Chen]

Hi, all,

On Tue, Apr 14, 2020 at 12:45 PM Jiaxun Yang <address@hidden> wrote:
>
> On Tue, 14 Apr 2020 09:40:26 +0800
> maobibo <address@hidden> wrote:
>
> > On 04/13/2020 04:18 PM, Jiaxun Yang wrote:
> > > On Mon, 13 Apr 2020 15:30:09 +0800
> > > Huacai Chen <address@hidden> wrote:
> > >
> > >> We are preparing to add KVM support for Loongson-3. VZ extension is
> > >> fully supported in Loongson-3A R4+, and we will not care about old
> > >> CPUs (at least now). We already have a full functional Linux kernel
> > >> (based on Linux-5.4.x LTS) and QEMU (based on 5.0.0-rc2) and their
> > >> git repositories are here:
> > >>
> > >> QEMU: https://github.com/chenhuacai/qemu
> > >> Kernel: https://github.com/chenhuacai/linux
> > >>
> > >> Of course these two repositories need to be rework and not suitable
> > >> for upstream (especially the commits need to be splitted). We show
> > >> them here is just to tell others what we have done, and how
> > >> KVM/Loongson will look like.
> > >>
> > >> Our plan is make the KVM host side be upstream first, and after
> > >> that, we will make the KVM guest side and QEMU emulator be
> > >> upstream.
> > >
> > > + Aleksandar as QEMU/MIPS mainatiner
> > >
> > > I was involved in KVM/Loongson development a bit and also intend to
> > > help with mainline these works.
> > >
> > > After dealing with basic LS7A PCH kernel support, I'm going to
> > > cooperate with Huacai and anyone who interested in to deal with
> > > following stuff:
> > >
> > > - Basic QEMU/TCG support for Loongson64 instructions.
> > >     Well, it seems unrelated with KVM, but that would make
> > >     development easier with cross ISA emulation. I'm not going
> > > to implement all the features like Loongson's page table fast walk
> > >     extension and binary translation extension but I'll ensure
> > > any binary compiled with march=loongson3a can run flawlessly on
> > >     TCG.
> > >
> > > - Design of Loongson-VIRT QEMU machine
> > >     It is nearly impossible to bring a real Loongson system into
> > >     QEMU. Both RS780E and LS7A PCH have tons of unreasonable
> > > design that would make the emulation extremely complex, Loongson
> > >     company's KVM implementation[1] has already proofed that,
> > >     thay're now in the hell. So we all agreed that we should
> > > build a machine from draft. I think we should reuse existing infra
> > > as far as possible to reduce our work load. I'm planing to use
> > >     pci-host-cam-generic together with VIRTIO PCI devices and a
> > >     a strip down version of loongson,liointc-1.0a to build a
> > > pure PCI based system. But if any one have better idea please just
> > >     tell us, I'm still considering how to implement SMP-IPI and
> > > ACPI stuff.
>
> Hi Bibo,
> Thanks for your response.
>
> + Xing Li as I heard he is in charge of KVM from Loongson's news post.
>
> > It is a good job to add kvm virtualization support on loongson64
> > platform. I agree that we should define common virt machine hardware
> > system, however the compiled kernel binary should be the same with
> > host system, else it will bring out trouble for customers to
> > differentiate them between guest system and host system.
>
> I'm planing to use DeviceTree to pass device information between QEMU
> and guest kernel. So we can upgrade VM design at any moment without
> breaking Host Guest kernel compatibility.
>
>
> > For pci host bridge emulation, I suggest that gpex pcie host bridge
> > should be used, since it supports pcie hotplug and arm/riscv uses
> > this pcie host bridge.
>
>
> gpex is basically a pci-host-cam-generic at kernel point of view. I'm
> planing to reuse it too.
I agree to use GPEX, and the qemu in github is updated to use GPEX.

>
> >
> > For virtual interrupt controller, it should support MSI/MSIX
> > interrupt, irqchip in kernel, IRQFD, vhost/vfio etc. I have no idea
> > how to define virtual interrupt controller now.
>
> Yes, APIC from x86 and GIC from Arm are all bonded closely with their
> architecture so we can't reuse them. Probably what we need is a
> modified version of EXTIOI from Loongson-3A4000.
>
> Does Loongson have a plan to implement hardware virtual irqchip? If so
> we must align with it's design.
>
> My plan is we can firstly implement a very simple IRQCHIP instead of
> complex one which only handle UART and PCI INTx. That is enough to make
> the system work. After that we can sit and discuss how to implement a
> complicated version to archive more features.
>
> >
> >
> > regards
> > bibo,mao
> >
> [...]