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Re: Masking all interrupts in TCG mode

From: Peter Maydell
Subject: Re: Masking all interrupts in TCG mode
Date: Fri, 2 Oct 2020 19:09:18 +0100

On Fri, 2 Oct 2020 at 17:50, Arnabjyoti Kalita
<akalita@cs.stonybrook.edu> wrote:
> What I can understand is that when we restore the VM State, the same 
> interrupt state will be restored which was before we did a savevm. And then 
> these interrupts will be executed appropriately.
> If there is an interrupt at the start of restore, then the interrupt will be 
> executed first before the process of executing and finding the TB starts, 
> based on the below logic. Am I correct ?
> while (!cpu_has_exception()) {
>     while (!cpu_has_interrupt()) {
>         tb = tb_find()
>         ....
>     }
> }

Yes, the interrupt will probably be the first thing to happen.
(If the VM save/restore had not happened, it would have been
the next thing to happen in the original execution.)

> Is it possible that the same interrupt could have different numbers
> in the KVM mode and in TCG mode? Like say, an interrupt is 0x15 in
> KVM, but is 0x75 in TCG.

I don't think that should happen. However, I'm not sure whether
the x86 guest code supports migration from KVM to TCG (I know that
it doesn't work for Arm guest code). KVM->KVM and TCG->TCG should
definitely both work.

-- PMM

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