Re: QEMU+KVM on RISC-V + Hypervisor Extension

[Anup Patel]

On Tue, Mar 15, 2022 at 12:18 PM Alistair Francis <alistair23@gmail.com> wrote:
>
> On Sun, Mar 13, 2022 at 12:12 PM Ralf Ramsauer
> <ralf.ramsauer@oth-regensburg.de> wrote:
> >
> > Hi,
> >
> > I'm trying to run Linux/QEMU+KVM inside an emulated
> > qemu-system-riscv64 VM (x86 host). On latest&greatest QEMU (1416688c53),
> > I run Linux inside QEMU. On host side:
> >
> > qemu-system-riscv64 -nographic \
> >          -machine virt \
> >          -cpu 'rv64,h=true' \
> >          -smp 8 -m 8G \
> >          -bios $latest_opensbi \
> >          -kernel $latest_upstream_linux \
> >         […snip…]
> >
> > Inside that machine, I boot Linux with KVM enabled:
> >
> > […]
> > [    0.228939] kvm [1]: hypervisor extension available
> > [    0.229000] kvm [1]: using Sv48x4 G-stage page table format
> > [    0.229033] kvm [1]: VMID 14 bits available
> > […]
> >
> > KVM seems to load correctly. Inside that machine, I compiled QEMU from
> > the same sources with the KVM accelerator enabled. When I try to start
> > QEMU with KVM enabled, I get
> >
> > ./qemu-system-riscv64 -nographic \
> >         -monitor none \
> >         -machine virt \
> >         -smp 1 -m 1G \
> >         -bios ./pc-bios/opensbi-riscv64-generic-fw_dynamic.bin \
> >         -serial stdio \
> >         -enable-kvm

The QEMU RISC-V KVM support is quite new so I haven't got a chance
to play with it.

Nevertheless, we should not pass any firmware when using KVM
so can you try "-bios none" ?

Regards,
Anup

> >
> > [ 4860.559194] kvm [9942]: VCPU exit error -95
> > [ 4860.584262] kvm [9942]: SEPC=0x0 SSTATUS=0x200004120 HSTATUS=0x2002001c0
> > [ 4860.586839] kvm [9942]: SCAUSE=0x14 STVAL=0x0 HTVAL=0x0 HTINST=0x0
> >
> > on the ringbuffer, together with a register dump of qemu [1] on the
> > console. Needless to say, but without -enable-kvm, it works fine.
> >
> > As far as I see that, SCAUSE=0x14 reports a 'Instruction Guest PF',
> > which would be kind of correct, if the guest's PC really tries to
> > execute at phys 0x0. DRAM of the 'virt' machine definition should start
> > at 0x80000000, where OpenSBI resides. So I wonder if an erroneous reset
> > PC might be the culprit…
> >
> > Before digging deeper into that issue, I wanted to ask if Qemu/KVM
> > inside an emulated riscv64+H-extension is actually supported, or if this
> > is a known bug and has some ongoing work.
>
> RISC-V KVM should work. I haven't had a chance to try it myself though.
>
> I have CCed two people who hopefully can help.
>
> Alistair
>
> >
> > Thanks
> >    Ralf
> >
> > [1]
> >
> >   pc       0000000000000000
> >   mhartid  0000000000000000
> >   mstatus  0000000200000000
> >   mip      0000000000000000
> >   mie      0000000000000000
> >   mideleg  0000000000000000
> >   medeleg  0000000000000000
> >   mtvec    0000000000000000
> >   stvec    0000000000000000
> >   mepc     0000000000000000
> >   sepc     0000000000000000
> >   mcause   0000000000000000
> >   scause   0000000000000000
> >   mtval    0000000000000000
> >   stval    0000000000000000
> >   mscratch 0000000000000000
> >   sscratch 0000000000000000
> >   satp     0000000000000000
> >   x0/zero  0000000000000000 x1/ra    0000000000000000 x2/sp
> > 0000000000000000 x3/gp    0000000000000000
> >   x4/tp    0000000000000000 x5/t0    0000000000000000 x6/t1
> > 0000000000000000 x7/t2    0000000000000000
> >   x8/s0    0000000000000000 x9/s1    0000000000000000 x10/a0
> > 0000000000000000 x11/a1   00000000bf000000
> >   x12/a2   0000000000000000 x13/a3   0000000000000000 x14/a4
> > 0000000000000000 x15/a5   0000000000000000
> >   x16/a6   0000000000000000 x17/a7   0000000000000000 x18/s2
> > 0000000000000000 x19/s3   0000000000000000
> >   x20/s4   0000000000000000 x21/s5   0000000000000000 x22/s6
> > 0000000000000000 x23/s7   0000000000000000
> >   x24/s8   0000000000000000 x25/s9   0000000000000000 x26/s10
> > 0000000000000000 x27/s11  0000000000000000
> >   x28/t3   0000000000000000 x29/t4   0000000000000000 x30/t5
> > 0000000000000000 x31/t6   0000000000000000
> >