Re: [PATCH v3 00/26] Implementing a MSHV (Microsoft Hypervisor) accelerator

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Aug 07, 2025 at 04:39:25PM +0200, Magnus Kulke wrote:
> Hey all,
> 
> This is the third revision of a patch set implementing an accelerator
> for the MSHV kernel driver, exposing HyperV to Linux "Dom0" hosts in various
> scenarios. Thank you for the feedback so far. Since the last revision we
> incorporated feedback from the last review and identified further areas for
> performance fixes, notably in the irqfd handling. I'm looking forward to your
> comments.
> 
> Best regards,
> 
> magnus


So regarding merging plans. Did you guys get in touch
with Sunil? That's the easiest smoothest path, through
an existing maintainer.


> Changelog:
> 
> v2 => v3
> 
> - Addressed code review comments (style)
> - Reserve GSI 01-23 for IO-APIC pins (this resolved a problem in which MSI
>   routes would be overwritten with interrupts from legacy devices, breaking
>   irqfd notification for virtio-blk queues)
> - Guard memory slot table with mutex and RCU mechanism (multiple threads
>   might access the memory slot table, and in the event of an UNMAPPED_GPA
>   exit we need to query the table for an unmapped region covering that GPA)
> - Include memory slot manager in MshvState
> - Produce mshv.h kernel header with ./scripts/update-linux-headers.sh from
>   linux 6.16 (not all UAPI definitions are defined in the upstream kernel,
>   hence we ship hw/hyper/hvgdk*.h and hw/hyperv/hvhdk*.h headers)
> - Added a QMP command query-mshv (a requirement for integration into
>   higher-level tooling)
> - Removed handling of HALT vm exit, since this is not a supported HV
>   message any more.
> - Added 2 maintainers from Microsoft for the respective file hierarchy
> - Added mshv as accelerator option in the documentation
> 
> RFC (v1) => v2
> 
> - Addressed code review comments (style, consilidation).
> - Rewrote the logic that handles overlap-in-userspace mappings to use
>   a static list of slots, inspired by the HVF accelerator code.
> - Fixed a bug that wrote corrupt payload in a MSHV_SET_MSI_ROUTING
>   call, preventing vhost=on to work on tap network devices.
> - Removed an erronous truncation of guest addresses to 32bit when
>   registering ioeventfd's using MSHV_IOEVENTFD. This resulted in
>   shadowing of low memory when ioevents were registered with
>   addresses beyond the 4gb barrier and thus unexpected "unmapped gpa"
>   vm exits in lower mem regions (impacting io performance).
> - Fixed problem in which the MSI routing table was committed for KVM
>   KVM instead of MSHV in virtio-pci bus initialization.
> - Added handler for HLT vm exits.
> - The above fixes removed a few limitation present in the previous
>   revision:
>   - Guest with machine type "pc" are booting (testing is still mostly
>     performed with q35)
>   - Tap network devices can be used with vhost=on option.
>   - Seabios can be used with >2.75G memory and multiple virtio-pci
>     devices
>   - I/O performance improvement as extranous MMIO vm exits are avoided
>     by registering ioevents with a correct address.
> 
> Notes:
> 
> - A discrete kernel ioctl "set_immediate_exit" (to avoid a race condition
>   when handling terminiation signals like ctrl-a x) has been tested and
>   proven to mitigate the problem. Since other consumers of /dev/mshv have
>   simular requirements as QEMU, we opted to iterate a bit more on the
>   respective kernel interface.
> 
> Magnus Kulke (25):
>   accel: Add Meson and config support for MSHV accelerator
>   target/i386/emulate: Allow instruction decoding from stream
>   target/i386/mshv: Add x86 decoder/emu implementation
>   hw/intc: Generalize APIC helper names from kvm_* to accel_*
>   include/hw/hyperv: Add MSHV ABI header definitions
>   linux-headers/linux: Add mshv.h headers
>   accel/mshv: Add accelerator skeleton
>   accel/mshv: Register memory region listeners
>   accel/mshv: Initialize VM partition
>   accel/mshv: Add vCPU creation and execution loop
>   accel/mshv: Add vCPU signal handling
>   target/i386/mshv: Add CPU create and remove logic
>   target/i386/mshv: Implement mshv_store_regs()
>   target/i386/mshv: Implement mshv_get_standard_regs()
>   target/i386/mshv: Implement mshv_get_special_regs()
>   target/i386/mshv: Implement mshv_arch_put_registers()
>   target/i386/mshv: Set local interrupt controller state
>   target/i386/mshv: Register CPUID entries with MSHV
>   target/i386/mshv: Register MSRs with MSHV
>   target/i386/mshv: Integrate x86 instruction decoder/emulator
>   target/i386/mshv: Write MSRs to the hypervisor
>   target/i386/mshv: Implement mshv_vcpu_run()
>   accel/mshv: Handle overlapping mem mappings
>   docs: Add mshv to documentation
>   MAINTAINERS: Add maintainers for mshv accelerator
> 
> Praveen K Paladugu (1):
>   qapi/accel: Allow to query mshv capabilities
> 
>  MAINTAINERS                      |   15 +
>  accel/Kconfig                    |    3 +
>  accel/accel-irq.c                |  106 ++
>  accel/meson.build                |    3 +-
>  accel/mshv/irq.c                 |  397 +++++++
>  accel/mshv/mem.c                 |  562 ++++++++++
>  accel/mshv/meson.build           |    9 +
>  accel/mshv/mshv-all.c            |  726 +++++++++++++
>  accel/mshv/msr.c                 |  373 +++++++
>  accel/mshv/trace-events          |   30 +
>  accel/mshv/trace.h               |   14 +
>  docs/devel/codebase.rst          |    2 +-
>  hw/core/machine-qmp-cmds.c       |   14 +
>  hw/intc/apic.c                   |    8 +
>  hw/intc/ioapic.c                 |   20 +-
>  hw/virtio/virtio-pci.c           |   21 +-
>  include/hw/hyperv/hvgdk.h        |   19 +
>  include/hw/hyperv/hvgdk_mini.h   |  864 +++++++++++++++
>  include/hw/hyperv/hvhdk.h        |  164 +++
>  include/hw/hyperv/hvhdk_mini.h   |  105 ++
>  include/system/accel-irq.h       |   37 +
>  include/system/mshv.h            |  195 ++++
>  linux-headers/linux/mshv.h       |  291 ++++++
>  meson.build                      |   11 +
>  meson_options.txt                |    2 +
>  qapi/accelerator.json            |   29 +
>  qemu-options.hx                  |   16 +-
>  scripts/meson-buildoptions.sh    |    3 +
>  scripts/update-linux-headers.sh  |    2 +-
>  target/i386/cpu.h                |    4 +-
>  target/i386/emulate/meson.build  |    7 +-
>  target/i386/emulate/x86_decode.c |   27 +-
>  target/i386/emulate/x86_decode.h |    9 +
>  target/i386/emulate/x86_emu.c    |    3 +-
>  target/i386/emulate/x86_emu.h    |    2 +
>  target/i386/meson.build          |    2 +
>  target/i386/mshv/meson.build     |    8 +
>  target/i386/mshv/mshv-cpu.c      | 1674 ++++++++++++++++++++++++++++++
>  target/i386/mshv/x86.c           |  297 ++++++
>  39 files changed, 6038 insertions(+), 36 deletions(-)
>  create mode 100644 accel/accel-irq.c
>  create mode 100644 accel/mshv/irq.c
>  create mode 100644 accel/mshv/mem.c
>  create mode 100644 accel/mshv/meson.build
>  create mode 100644 accel/mshv/mshv-all.c
>  create mode 100644 accel/mshv/msr.c
>  create mode 100644 accel/mshv/trace-events
>  create mode 100644 accel/mshv/trace.h
>  create mode 100644 include/hw/hyperv/hvgdk.h
>  create mode 100644 include/hw/hyperv/hvgdk_mini.h
>  create mode 100644 include/hw/hyperv/hvhdk.h
>  create mode 100644 include/hw/hyperv/hvhdk_mini.h
>  create mode 100644 include/system/accel-irq.h
>  create mode 100644 include/system/mshv.h
>  create mode 100644 linux-headers/linux/mshv.h
>  create mode 100644 target/i386/mshv/meson.build
>  create mode 100644 target/i386/mshv/mshv-cpu.c
>  create mode 100644 target/i386/mshv/x86.c
> 
> -- 
> 2.34.1