* Avi Kivity <[email protected]> wrote:
> I would like to remove this limitation. I see several ways to go about
> it:
>
> 1. Drop the use of IST
>
> This would reduce the (perceived) reliability of the kernel and would
> probably not be welcomed.
> hpa/Ingo, any opinions?
i think we should actually do #1 unconditionally.
ISTs are bad for the native kernel too. They have various nasty
complications in the stack walker (and hence they _reduce_ reliability in
practice), and they are non-preemptible as well. Plus we have the
maximum-stack-footprint ftrace plugin now, which can remove any perception
about how bad the worst-case stack footprint is in practice.
If it ever becomes an issue we could also soft-switch to a larger (per
CPU) exception stack from the exception handlers themselves. The
architectural stack footprint of the various critical exceptions are
calculatable and low - so we could switch away and get almost the kind of
separation that ISTs give. There's no deep reason to actually make use of
hw switched ISTs.
So feel free to send a patch that just standardizes the critical
exceptions to use the regular kernel stack. (I havent actually tried this
but it should be relatively simple to implement. Roadblocks are possible.)
Ingo
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