[coreboot] question on SMM

[ron minnich]

On Fri, Jun 30, 2017 at 4:28 PM Nico Huber <nico.h at gmx.de> wrote:

>
>
> Sounds really doable, but I'm a bit confused here, maybe because I
> didn't look at SMM handlers for some time. Did you evaluate if you
> need SMM at all? I just thought if you add board specific code to
> the kernel, why would you have to do anything in SMM? In the case
> of ACPI, most interrupts are already directly routed to the kernel
> (as SCI instead of SMI).
>
>
That would be optimal -- just turn it off. We're seeing a problem with
linux startup, while booting no smm enabled, where Linux really wants to do
that OSL nonsense via SMI for ACPI. Can we really configure hardware such
that an SMI is impossible, and will Linux continue to work if we do?

I like your idea a lot -- just do whatever it takes to make SMM interrupts
turn into normal SCI -- I just don't know for sure it's possible to make it
happen. But I'll look.

The remaining problem is the "security" offered by having an SMI gatekeeper
on the flash. Given the history of such "security" approaches, I suspect
we're better off without them. BUT, there is concern that if we don't use
these approaches, there are scenarios where flash gets written by the wrong
people.



> Also, if you are going to reimplement the vendor ACPI tables, why
> not write kernel-native drivers? ACPI is just a weird OS-independent
> way of writing drivers.
>

I agree with you here, but we can only kill one dragon at a time.

We ran supercomputers at LANL for years, up until 2010 or so, with no SMM
and ACPI and all was well. I've never quite figured out what problem SMI
and ACPI solved that could not have been solved better in other ways.

ron
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