Re: [Qemu-devel] [RFC PATCH v2 00/21] Guest exploitation of the XIVE interrupt controller (POWER9)

[David Gibson]

On Mon, Sep 11, 2017 at 07:12:14PM +0200, Cédric Le Goater wrote:
> On a POWER9 sPAPR machine, the Client Architecture Support (CAS)
> negotiation process determines whether the guest operates with an
> interrupt controller using the XICS legacy model, as found on POWER8,
> or in XIVE exploitation mode, the newer POWER9 interrupt model. This
> patchset is a proposal to add XIVE support in POWER9 sPAPR machine.
> 
> Follows a model for the XIVE interrupt controller and support for the
> Hypervisor's calls which are used to configure the interrupt sources
> and the event/notification queues of the guest. The last patch
> integrates XIVE in the sPAPR machine.
> 
> Code is here:


An overall comment:

I note in several replies here that I think the way XICS objects are
re-used for XIVE is really ugly, and I think it will make future
maintenance pretty painful.

I'm thinking maybe trying to support the CAS negotiation of interrupt
controller from day 1 is warping the design.  A better approach might
be first to implement XIVE only when given a specific machine option -
guest gets one or the other and can't negotiate.

That should allow a more natural XIVE design to emerge, *then* we can
look at what's necessary to make boot-time negotiation possible.
> 
>   https://github.com/legoater/qemu/commits/xive
> 
> Caveats :
> 
>  - IRQ allocator : making progress
> 
>    The sPAPR machine make uses of the interrupt controller very early
>    in the initialization sequence to allocate IRQ numbers and populate
>    the device tree. CAS requires XIVE to be able to switch interrupt
>    model and consequently have the models share a common IRQ allocator.   
> 
>    I have chosen to link the sPAPR XICS interrupt source into XIVE to
>    share the ICSIRQState array which acts as an IRQ allocator. This
>    can be improved.
> 
>  - Interrupt presenter :
> 
>    The register data is directly stored under the ICPState structure
>    which is shared with all other sPAPR interrupt controller models.
> 
>  - KVM support : not addressed yet
> 
>    The guest needs to be run with kernel_irqchip=off on a POWER9 system.
> 
>  - LSI : lightly tested.
>    
> Thanks,
> 
> C.
> 
> Changes since RFC v1:
> 
>  - removed initial complexity due to a tentative try to support
>    PowerNV. This will come later.
>  - removed specific XIVE interrupt source and presenter models
>  - renamed files and typedefs
>  - removed print_info() handler
>  - introduced a CAS reset to rebuild the device tree
>  - linked the XIVE model with the sPAPR XICS interrupt source to share
>    the IRQ allocator   
>  - improved hcall support (still some missing but they are not used
>    under Linux)
>  - improved device tree
>  - should have addressed comments in first RFC
>  - and much more ... Next version should have a better changelog.
>  
> 
> Cédric Le Goater (21):
>   ppc/xive: introduce a skeleton for the sPAPR XIVE interrupt controller
>   migration: add VMSTATE_STRUCT_VARRAY_UINT32_ALLOC
>   ppc/xive: define the XIVE internal tables
>   ppc/xive: provide a link to the sPAPR ICS object under XIVE
>   ppc/xive: allocate IRQ numbers for the IPIs
>   ppc/xive: introduce handlers for interrupt sources
>   ppc/xive: add MMIO handlers for the XIVE interrupt sources
>   ppc/xive: describe the XIVE interrupt source flags
>   ppc/xive: extend the interrupt presenter model for XIVE
>   ppc/xive: add MMIO handlers for the XIVE TIMA
>   ppc/xive: push the EQ data in OS event queue
>   ppc/xive: notify the CPU when interrupt priority is more privileged
>   ppc/xive: handle interrupt acknowledgment by the O/S
>   ppc/xive: add support for the SET_OS_PENDING command
>   spapr: modify spapr_populate_pci_dt() to use a 'nr_irqs' argument
>   spapr: add a XIVE object to the sPAPR machine
>   ppc/xive: add hcalls support
>   ppc/xive: add device tree support
>   ppc/xive: introduce a helper to map the XIVE memory regions
>   ppc/xics: introduce a qirq_get() helper in the XICSFabric
>   spapr: activate XIVE exploitation mode
> 
>  default-configs/ppc64-softmmu.mak |   1 +
>  hw/intc/Makefile.objs             |   1 +
>  hw/intc/spapr_xive.c              | 821 +++++++++++++++++++++++++++++++++
>  hw/intc/spapr_xive_hcall.c        | 930 
> ++++++++++++++++++++++++++++++++++++++
>  hw/intc/xics.c                    |  11 +-
>  hw/intc/xive-internal.h           | 189 ++++++++
>  hw/ppc/spapr.c                    | 110 ++++-
>  hw/ppc/spapr_hcall.c              |   6 +
>  hw/ppc/spapr_pci.c                |   4 +-
>  include/hw/pci-host/spapr.h       |   2 +-
>  include/hw/ppc/spapr.h            |  17 +-
>  include/hw/ppc/spapr_xive.h       |  75 +++
>  include/hw/ppc/xics.h             |   7 +
>  include/migration/vmstate.h       |  10 +
>  14 files changed, 2169 insertions(+), 15 deletions(-)
>  create mode 100644 hw/intc/spapr_xive.c
>  create mode 100644 hw/intc/spapr_xive_hcall.c
>  create mode 100644 hw/intc/xive-internal.h
>  create mode 100644 include/hw/ppc/spapr_xive.h
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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