Re: [RFC v3 0/5] Introduce MMIO/PIO dispatch file descriptors (ioregionfd)

[Paolo Bonzini <pbonzini@redhat.com>]

On 21/02/21 13:04, Elena Afanasova wrote:
> This patchset introduces a KVM dispatch mechanism which can be used
> for handling MMIO/PIO accesses over file descriptors without returning
> from ioctl(KVM_RUN). This allows device emulation to run in another task
> separate from the vCPU task.
> 
> This is achieved through KVM vm ioctl for registering MMIO/PIO regions and
> a wire protocol that KVM uses to communicate with a task handling an
> MMIO/PIO access.
> 
> TODOs:
> * Implement KVM_EXIT_IOREGIONFD_FAILURE
> * Add non-x86 arch support
> * Add kvm-unittests
> * Flush waiters if ioregion is deleted

Hi ELena,

as a quick thing that jumped at me before starting the review, you 
should add a test for the new API in tools/testing/selftests/kvm, as 
well as documentation.  Ideally, patch 4 would also add a testcase that 
fails before and passes afterwards.

Also, does this work already with io_uring?

Paolo

> v3:
>   - add FAST_MMIO bus support
>   - add KVM_IOREGION_DEASSIGN flag
>   - rename kvm_ioregion read/write file descriptors
>   - split ioregionfd signal handling support into two patches
>   - move ioregion_interrupted flag to ioregion_ctx
>   - reorder ioregion_ctx fields
>   - rework complete_ioregion operations
>   - add signal handling support for crossing a page boundary case
>   - change wire protocol license
>   - fix ioregionfd state machine
>   - remove ioregionfd_cmd info and drop appropriate macros
>   - add comment on ioregionfd cmds/replies serialization
>   - drop kvm_io_bus_finish/prepare()
> 
> Elena Afanasova (5):
>    KVM: add initial support for KVM_SET_IOREGION
>    KVM: x86: add support for ioregionfd signal handling
>    KVM: implement wire protocol
>    KVM: add ioregionfd context
>    KVM: enforce NR_IOBUS_DEVS limit if kmemcg is disabled
> 
>   arch/x86/kvm/Kconfig          |   1 +
>   arch/x86/kvm/Makefile         |   1 +
>   arch/x86/kvm/vmx/vmx.c        |  40 ++-
>   arch/x86/kvm/x86.c            | 273 +++++++++++++++++-
>   include/linux/kvm_host.h      |  28 ++
>   include/uapi/linux/ioregion.h |  30 ++
>   include/uapi/linux/kvm.h      |  25 ++
>   virt/kvm/Kconfig              |   3 +
>   virt/kvm/eventfd.c            |  25 ++
>   virt/kvm/eventfd.h            |  14 +
>   virt/kvm/ioregion.c           | 529 ++++++++++++++++++++++++++++++++++
>   virt/kvm/ioregion.h           |  15 +
>   virt/kvm/kvm_main.c           |  36 ++-
>   13 files changed, 996 insertions(+), 24 deletions(-)
>   create mode 100644 include/uapi/linux/ioregion.h
>   create mode 100644 virt/kvm/eventfd.h
>   create mode 100644 virt/kvm/ioregion.c
>   create mode 100644 virt/kvm/ioregion.h
>