hyperv/vmbus: static assign IDT vector for hv

[howard0su_gmail.com]

Summary

It is not needed to dynamic allocate idt vector. Instead,
reuse the vector of XENHVM since both cannot co-exist.

EVTCHN naming also apply to HYPERV since the interrupt is used to raise event as well.

[royger]

How does this interact with D5291? AFAICT they are not compatible. In any case, IDT_EVTCHN should be renamed to IDT_HYPERVISOR.

[howard0su_gmail.com]

update local_apic code to mark IDT_EVTCHN is used when HYPERV is enabled.

[royger]

IMHO this IDT vector needs to be renamed to something that's not Xen-specific for HyperV to use it.

[sepherosa_gmail.com]

In D5254#115151, @royger wrote:

IMHO this IDT vector needs to be renamed to something that's not Xen-specific for HyperV to use it.

We had a brainstorm last week, talked about the name. One funny thing is that in hyper-v, the interrupt vector is also used to service event, so we think EVTCHN seems fine :)

[howard0su_gmail.com]

Shall we commit this without changing the IDT name?

[decui_microsoft.com]

In D5254#120056, @howard0su_gmail.com wrote:

Shall we commit this without changing the IDT name?

I would suggest we use IDT_HYPERVISOR as Roger mentioned.

Event Channel is a terminology in Xen's context.
On VMBus Channel, the interrupts are for both VMBus Events and VMBus Messages, so IDE_EVTCHN is a little misleading in Hyper-V's context.

[howard0su_gmail.com]

Rebase to master. Rename {IDT|IRQ}_EVTCHN to _HYPERVISOR

[decui_microsoft.com]

LGTM

sys/x86/include/segments.h

216 ↗

(On Diff #14293)

We need to update the comment too :-)
It can be something like "Vector on which hypervisor interrupt is delivered"

[sepherosa_gmail.com]

amd64/machdep.c:

#ifdef XENHVM
setidt(IDT_EVTCHN, &IDTVEC(xen_intr_upcall), SDT_SYSIGT, SEL_UPL, 0);
#endif

I have considered a bit about how to handle this in a nice way. May be we need IDT_HYPERVISOR{1,2,3,4}? Define IDT_EVTCHAN as an alias to HYPERVISOR1, and IDT_HYPERV to HYPERVISOR2 etc. So this could be handled nicely. Else it would look pretty confusing at least to me, i.e. we override it later.

[howard0su_gmail.com]

fix comment

[howard0su_gmail.com]

Add jhb@ to seek for input on IDT thing