Re: [RFC v2 00/14] Add SDEI support for arm64

[Guoheyi <guoheyi@huawei.com>]

Hi Peter,

Could you spare some time to review the framework and provide comments 
and advice?

Thanks,

HG


On 2019/11/5 17:10, Heyi Guo wrote:
> SDEI is for ARM "Software Delegated Exception Interface". AS ARM64 doesn't have
> native non-maskable interrupt (NMI), we rely on higher privileged (larger
> exception level) software to change the execution flow of lower privileged
> (smaller exception level) software when certain events occur, to emulate NMI
> mechanism, and SDEI is the standard interfaces between the two levels of
> privileged software. It is based on SMC/HVC calls.
>
> The higher privileged software implements an SDEI dispatcher to handle SDEI
> related SMC/HVC calls and trigger SDEI events; the lower privileged software
> implements an SDEI client to request SDEI services and handle SDEI events.
>
> Core interfaces provided by SDEI include:
>
> 1. interrupt bind: client can request to bind an interrupt to an SDEI event, so
> the interrupt will be a non-maskable event and the event number will be returned
> to the caller. Only PPI and SPI can be bound to SDEI events.
>
> 2. register: client can request to register a handler to an SDEI event, so
> dispatcher will change PC of lower privileged software to this handler when
> certain event occurs.
>
> 3. complete: client notifies dispatcher that it has completed the event
> handling, so dispatcher will restore the context of guest when it is
> interrupted.
>
> In virtualization situation, guest OS is the lower privileged software and
> hypervisor is the higher one.
>
> KVM is supposed to pass SMC/HVC calls to qemu, and qemu will emulate an SDEI
> dispatcher to serve the SDEI requests and trigger the events. If an interrupt is
> requested to be bound to an event, qemu should not inject the interrupt to guest
> any more; instead, it should save the context of VCPU and change the PC to event
> handler which is registered by guest, and then return to guest.
>
> To make the conversion of interrupt to SDEI event transparent to other modules
> in qemu, we used qemu_irq and qemu_irq_intercept_in() to override the default
> irq handler with SDEI event trigger. I saw qemu_irq_intercept_in() should be
> only used in qemu MST, but it seemed fit to override interrupt injection with
> event trigger after guest requests to bind interrupt to SDEI event.
>
> This patchset is trying to implement the whole SDEI framework in qemu with KVM
> enabled, including all SDEI v1.0 interfaces, as well as event trigger conduit
> from other qemu devices after interrupt binding.
>
> Key points:
> - We propose to only support kvm enabled arm64 virtual machines, for
>    non-kvm VMs can emulate EL3 and have Trusted Firmware run on it,
>    which has a builtin SDEI dispatcher.
> - New kvm capability KVM_CAP_FORWARD_HYPERCALL is added to probe if
>    kvm supports forwarding hypercalls, and the capability should be
>    enabled explicitly.
> - We make the dispatcher as a logical device, to save the states
>    during migration or save/restore operation; only one instance is
>    allowed in one VM.
> - We use qemu_irq as the bridge for other qemu modules to switch from
>    irq injection to SDEI event trigger after VM binds the interrupt to
>    SDEI event. We use qemu_irq_intercept_in() to override qemu_irq
>    handler with SDEI event trigger, and a new interface
>    qemu_irq_remove_intercept() is added to restore the handler to
>    default one (i.e. ARM GIC).
>
> More details are in the commit message of each patch.
>
> Basic tests are done by emulating a watchdog timer and triggering SDEI
> event in every 10s.
>
> Please focus on the interfaces and framework first. We can refine the code for
> several rounds after the big things have been determined.
>
> Any comment or suggestion is welcome.
>
> Thanks,
>
> HG
>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: Dave Martin <Dave.Martin@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Cornelia Huck <cohuck@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Shannon Zhao <shannon.zhaosl@gmail.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
>
> v2:
> - Import import linux/arm_sdei.h to standard-headers
> - Drop SDEI table definition and add comments
> - Some bugfix and code refinement
>
> Heyi Guo (14):
>    update-linux-headers.sh: import linux/arm_sdei.h to standard-headers
>    standard-headers: import arm_sdei.h
>    arm/sdei: add virtual device framework
>    arm: add CONFIG_SDEI build flag
>    arm/sdei: add support to handle SDEI requests from guest
>    arm/sdei: add system reset callback
>    arm/sdei: add support to trigger event by GIC interrupt ID
>    core/irq: add qemu_irq_remove_intercept interface
>    arm/sdei: override qemu_irq handler when binding interrupt
>    arm/sdei: add support to register interrupt bind notifier
>    linux-headers/kvm.h: add capability to forward hypercall
>    arm/sdei: add stub to fix build failure when SDEI is not enabled
>    arm/kvm: handle guest exit of hypercall
>    virt/acpi: add SDEI table if SDEI is enabled
>
>   default-configs/arm-softmmu.mak           |    1 +
>   hw/arm/Kconfig                            |    4 +
>   hw/arm/virt-acpi-build.c                  |   26 +
>   hw/core/irq.c                             |   11 +
>   include/hw/irq.h                          |    8 +-
>   include/standard-headers/linux/arm_sdei.h |   73 +
>   linux-headers/linux/kvm.h                 |    1 +
>   scripts/update-linux-headers.sh           |    1 +
>   target/arm/Makefile.objs                  |    4 +
>   target/arm/kvm.c                          |   17 +
>   target/arm/sdei-stub.c                    |   49 +
>   target/arm/sdei.c                         | 1576 +++++++++++++++++++++
>   target/arm/sdei.h                         |   60 +
>   target/arm/sdei_int.h                     |  121 ++
>   14 files changed, 1950 insertions(+), 2 deletions(-)
>   create mode 100644 include/standard-headers/linux/arm_sdei.h
>   create mode 100644 target/arm/sdei-stub.c
>   create mode 100644 target/arm/sdei.c
>   create mode 100644 target/arm/sdei.h
>   create mode 100644 target/arm/sdei_int.h
>