Re: [PATCH v2 0/8] riscv: AIA: kernel-irqchip=off support

[Kashyap Chamarthy <kchamart@redhat.com>]

On Mon, Feb 24, 2025 at 04:24:07PM +0800, Yong-Xuan Wang wrote:
> This series introduces the user-space AIA MSI emulation when using KVM
> acceleration.
> 
> After this series, RISC-V QEMU virt machine with KVM acceleration has
> 3 parameters to control the type of irqchip and its emulation method:
> - Machine prop "aia" controls the type of irqchip
>   - none: use PLIC and emulated in user-space
>   - aplic: use AIA wired and emulated in user-space
>   - aplic-imsic: use AIA MSI, emulation mode is determined by
>     "kernel-irqchip" and "riscv-aia". This can only be used
>     when the host machine support the AIA extension.
> - Accel prop "kernel-irqchip", effective with AIA MSI
>   - on: in-kernel APLIC and in-kernel IMSIC
>   - off: user-space APLIC and user-space IMSIC
>   - split: user-space APLIC and in-kernel IMSIC
> - Accel prop "riscv-aia", effective with in-kernel IMSIC
>   - emul: use MRIF as in-kernel IMSIC
>   - hw: use hardware guest IMSIC file as in-kernel IMSIC
>   - auto: use the hardware guest IMSICs whenever available otherwise
>     fallback to MRIF

[...]

> Yong-Xuan Wang (8):
>   target/riscv/kvm: rewrite get/set for KVM_REG_RISCV_CSR
>   target/riscv/kvm: add KVM_REG_RISCV_CSR_AIA
>   target/riscv/kvm: add KVM_REG_RISCV_CSR_SMSTATEEN
>   target/riscv: add helper to get CSR name
>   target/riscv/kvm: rewrite kvm_riscv_handle_csr
>   target/riscv/kvm: add CSR_SIREG and CSR_STOPEI emulation
>   docs: update the description about RISC-V AIA
>   hw/intc/imsic: prevent to use IMSIC when host doesn't support AIA
>     extension
> 
>  docs/specs/riscv-aia.rst   |  24 +++-
>  docs/system/riscv/virt.rst |  10 +-
>  hw/intc/riscv_imsic.c      |  17 ++-
>  target/riscv/cpu.h         |  10 +-
>  target/riscv/csr.c         |  30 ++---
>  target/riscv/kvm/kvm-cpu.c | 235 +++++++++++++++++++++++++++++++------
>  6 files changed, 254 insertions(+), 72 deletions(-)


I don't pretend to grok all the details here, and I couldn't test the
KVM-acceleration path ("-accel kvm,kernel-irqchip=split"), as I don't
yet have hardware to test.  I was able to test the TCG part:

I'm at:

    $> git describe
    v9.2.0-1976-g68d58113df

My QEMU command-line is here[1].  I tried out these two variataions:

    ... -machine virt,accel=tcg,aia=aplic,kernel-irqchip=split ...

    ... -machine virt,accel=tcg,aia=aplic-imsic,kernel-irqchip=split ...

And booted a Fedora-41 RISC-V host-generic guest image from here:

    https://dl.fedoraproject.org/pub/alt/risc-v/release/41/Server/riscv64/images/

As near as I see, nothing exploded :)

I see that:

  - From the docs: “aia=aplic” selects APLIC (advanced platform level
    interrupt controller) to handle wired interrupts whereas the
    “aia=aplic-imsic” selects APLIC and IMSIC (incoming message signaled
    interrupt controller) to handle both wired interrupts and MSIs

  - There's no user-visible change here, but only a developer-visible
    change: in terms of what's being emulated in userspace vs. in-kernel
    irqchip.)

So, if it's still not too late:

    Tested-by: Kashyap Chamarthy <kchamart@redhat.com>

        * * *

[1] QEMU command-line:
------------------------------------------------------------------------
$ ./qemu-system-riscv64
-display none
-cpu max
-no-user-config
-nodefaults
-serial stdio
-smp 4,sockets=4,cores=1,threads=1
-machine virt,accel=tcg,aia=aplic,kernel-irqchip=split
-blockdev node-name=node-Base1,driver=raw,file.driver=file,file.filename=./base1.raw,file.node-name=node-Base1-file
-device virtio-blk,drive=node-Base1,id=virtio0
-device virtio-net-device,netdev=net \
-netdev user,id=net,hostfwd=tcp::2222-:22 \
-blockdev '{"driver":"file","filename":"/usr/share/edk2/riscv/RISCV_VIRT_CODE.qcow2","node-name":"pflash0-storage","auto-read-only":true,"discard":"unmap"}' \
-blockdev '{"node-name":"pflash0-format","read-only":true,"driver":"qcow2","file":"pflash0-storage"}' \
-blockdev '{"driver":"file","filename":"/var/lib/libvirt/qemu/nvram/base1_VARS.qcow2","node-name":"pflash1-storage","auto-read-only":true,"discard":"unmap"}' \
-blockdev '{"node-name":"pflash1-format","read-only":false,"driver":"qcow2","file":"pflash1-storage"}' \
-machine virt,usb=off,dump-guest-core=off,memory-backend=riscv_virt_board.ram,pflash0=pflash0-format,pflash1=pflash1-format,acpi=off \
-m size=4194304k \
-object '{"qom-type":"memory-backend-ram","id":"riscv_virt_board.ram","size":4294967296}' \
-object rng-random,filename=/dev/urandom,id=rng \
-device virtio-rng-device,rng=rng 
------------------------------------------------------------------------

-- 
/kashyap