Re: [PATCH v3 1/3] xen/x86: add nmi continuation framework

[Jürgen Groß <jgross@xxxxxxxx>]

On 20.10.20 15:33, Jan Beulich wrote:
> On 16.10.2020 10:53, Juergen Gross wrote:
> > Actions in NMI context are rather limited as e.g. locking is rather
> > fragile.
> >
> > Add a generic framework to continue processing in normal interrupt
> > context after leaving NMI processing.
> >
> > This is done by a high priority interrupt vector triggered via a
> > self IPI from NMI context, which will then call the continuation
> > function specified during NMI handling.
> I'm concerned by there being just a single handler allowed, when
> the series already introduces two uses. A single NMI instance
> may signal multiple things in one go. At the very least we then
> need a priority, such that SERR could override oprofile.
A different approach could be not to introduce a generic interface,
but to explicitly call the continuation handlers in the interrupt
handler.

Instead of a function pointer, a parameter pointer and a busy
indicator (probably another function pointer) per cpu, we'd need for
now only a parameter value per cpu (for the oprofile case) and a
global flag (for the SERR case).

The downside would be having to add additional fields for other
use cases, but for now I think this could be the better way,
especially as this would remove the theoretical case of multiple
issues overwriting one another.

Thoughts?


Juergen