>>
>> One of the optimization, which can be used in pure SW is that
>> we can shadow APIC state as "RO" to guest so that all guest
>> read to APIC registers can run in full speed. T
>>
>>
>
>This can still be done with unacked interrupts: modify the
>state to "as
>if" the interrupt was injected, but commit it only if the injection
>succeeds. If injection fails, revert the change. It isn't very nice
>though.
Agree.
>
>Another possibility is:
>
> get_interrupt()
> ... do all sleepy things prior to injection
> enter critical section
> ack interrupt
> enter guest
>
Yes, that is safe and similar with current logic. Plus one condition:
if (real mode) for those sleepy things.
>> This optimization is probably cleaner & less-intrusive. Dynamic
>> patching to modify guest code could trigger mine sooner or later:(
>>
>>
>
>Dynamic patching is dangerous, but the only option to run
>Windows SMP on
>millions of machines out there.
I know:)
RO of APIC page can solve this issue in most case.
>
>>
>>> But the motivation here is not coding style, it's to be
>able to do the
>>> injection non-atomically. The tpr-opt patchset wants to write
>>> the tpr to
>>> memory, and that is a sleeping operation. Similarly, if we
>emulate big
>>> real mode we need to simulate interrupt injection by writing
>>> to the stack.
>>>
>>
>> OK. For big real mode has issue, that is very easy
>> to walk around, we can probably pre-load (pin) those 2 or 3 pages
>> before
>> injecting real mode irq.
>>
>
>Pinning has problems of its own. It can be made to work
>though. In any
>case, it can fail, so we need to ack the interrupt only after we have
>successfully pinned the page.
What I mean is we pre-load 2 pages where the stack are in, the logic may
be:
If (real mode)
get 2 pages.
enter critical path
....
VM Resume.
put these 2 pages.
handle VM Exit normally.
Since real mode is just a boot/install time isseu, performance is not
critical. This way doesn't hurt us.
thx,eddie
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