On 2019/9/30 21:15, Peter Maydell wrote:
> On Tue, 24 Sep 2019 at 16:23, Heyi Guo <guoheyi@huawei.com> wrote:
>> As promised, this is the first RFC patch set for arm64 SDEI support.
> Hi; for the benefit of possible reviewers who aren't familiar
> with every corner of the arm ecosystem, could you provide a
> summary of:
> * what is SDEI ?
SDEI is for ARM "Software Delegated Exception Interface". AS ARM64
doesn't have native non-maskable interrupt (NMI), we can rely on higher
privileged software to change the pc of lower privileged software on
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.
In virtualization situation, guest OS is the lower privileged software
and hypervisor is the higher one. Major interfaces provided by SDEI include:
1. interrupt bind: guest OS can request to bind an interrupt to an SDEI
event.
2. register: guest OS can request to register a handler to an SDEI
event, so hypervisor will change pc of guest to this handler when
certain event occurs.
3. complete: guest OS notifies hypervisor that it has completed the
event handling, so hypervisor will restore the context of guest when it
is interrupted.
> * what do KVM and QEMU want/need to do with it ?
KVM is supposed to pass SMC/HVC calls to qemu, and qemu will serve the
SDEI requests after parsing SMC/HVC calls. qemu also takes the
responsibility to 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.
> * what is this patchset trying to solve ?
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.
I will also provide the above context in the cover letter of v2 RFC.
Thanks,
Heyi
>
> That would provide some useful context for trying to
> review the patchset.
>
> thanks
> -- PMM
>
> .
>