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

[Elena Afanasova <eafanasova@gmail.com>]

On Sun, 2021-02-21 at 18:06 +0100, Paolo Bonzini wrote:
> 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,
> 

Hi Paolo,

Thank you for your answer.

> 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.
> 
Ok

> Also, does this work already with io_uring?
> 
I have a few kvm-unittests and QEMU testdev patch for testing base
functionality. I haven't tried to run them with io_uring (only run with
socket and pipes). Will do.

> 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
> >