On Sat, Apr 30, 2022 at 07:38:29PM +0800, Gavin Shan wrote:
Thank you for the comments and details. It should work by using bitmaps
to represent event's states. I will adopt your proposed structs in next
respin. However, there are more states needed. So I would adjust
"struct kvm_sdei_vcpu" like below in next respin.
struct kvm_sdei_vcpu {
unsigned long registered; /* the event is registered or not */
unsigned long enabled; /* the event is enabled or not */
unsigned long unregistering; /* the event is pending for unregistration */
I'm not following why we need to keep track of the 'pending unregister'
state directly. Is it not possible to infer from (active && !registered)?
unsigned long pending; /* the event is pending for delivery and handling */
unsigned long active; /* the event is currently being handled */
:
<this part is just like what you suggested>
};
I rename @pending to @unregister. Besides, there are two states added:
@pending: Indicate there has one event has been injected. The next step
for the event is to deliver it for handling. For one particular
event, we allow one pending event in the maximum.
Right, if an event retriggers when it is pending we still dispatch a
single event to the guest. And since we're only doing normal priority
events, it is entirely implementation defined which gets dispatched
first.
@active: Indicate the event is currently being handled. The information
stored in 'struct kvm_sdei_event_context' instance can be
correlated with the event.
Does this need to be a bitmap though? We can't ever have more than one
SDEI event active at a time since this is private to a vCPU.
Furthermore, it's fair enough to put the (vcpu) mask state into 'flags'
field of struct kvm_vcpu_arch :)
I think you can get away with putting active in there too, I don't see
why we need more than a single bit for this info.
Do we need this if we disallow nesting events?
Yes, we need this. "event == NULL" is used as indication of invalid
context. @event is the associated SDEI event when the context is
valid.
What if we use some other plumbing to indicate the state of the vCPU? MP
state comes to mind, for example.
Even the indication is done by another state, kvm_sdei_vcpu_context still
need to be linked (associated) with the event. After the vCPU context becomes
valid after the event is delivered, we still need to know the associated
event when some of hypercalls are triggered. SDEI_1_0_FN_SDEI_EVENT_COMPLETE
is one of the examples, we need to decrease struct kvm_sdei_event::event_count
for the hypercall.
Why do we need to keep track of how many times an event has been
signaled? Nothing in SDEI seems to suggest that the number of event
signals corresponds to the number of times the handler is invoked. In
fact, the documentation on SDEI_EVENT_SIGNAL corroborates this:
"""
The event has edgetriggered semantics and the number of event signals
may not correspond to the number of times the handler is invoked in the
target PE.
"""
DEN0054C 5.1.16.1
So perhaps we queue at most 1 pending event for the guest.
I'd also like to see if anyone else has thoughts on the topic, as I'd
hate for you to go back to the whiteboard again in the next spin.
Agreed. In next respin, we will have one pending event at most. Error
can be returned if user attempts to inject event whose pending state
(struct kvm_sdei_vcpu::pending) has been set.
I don't believe we can do that. The SDEI_EVENT_SIGNAL call should succeed,
even if the event was already pending.
Indeed, the hardest part is to determine the data structures and
functions we need. Oliver, your valuable comments are helping to
bring this series to the right track. However, I do think it's
helpful if somebody else can confirm the outcomes from the previous
discussions. I'm not sure if Marc has time for a quick scan and provide
comments.
I would summarize the outcomes from our discussions, to help Marc
or others to confirm:
Going to take a look at some of your later patches as well, just a heads
up.
- Drop support for the shared event.
- Dropsupport for the critical event.
- The events in the implementations are all private and can be signaled
(raised) by software.
- Drop migration support for now, and we will consider it using
pseudo firmware registers. So add-on patches are expected to support
the migration in future.
Migration will be supported in a future spin of this series, not a
subsequent one right? :) I had just made the suggestion because there was
a lot of renovations that we were discussing.
- Drop locking mechanism. All the functions are executed in vcpu context.
Well, not entirely. Just need to make sure atomics are used to post
events to another vCPU in the case of SDEI_EVENT_SIGNAL.
set_bit() fits the bill here, as we've discussed.
- To use the data struct as you suggested. Besides, the vcpu's mask
state is put to struct kvm_arch_vcpu::flags.
enum kvm_sdei_event
struct kvm_sdei_event_handler
struct kvm_sdei_event_context
struct kvm_sdei_vcpu