(Cc:-ing to lkml, because this might interest others too)
* Andi Kleen <[EMAIL PROTECTED]> wrote:
> > would be interesting to figure out what's going on here - i doubt
> > it's an ACPI bug, because then we'd be getting a hard page fault,
> > right? In
>
> ACPI hasn't changed at all in git-x86 and it worked fine before. So I
> don't really blame it.
yes, it did not change, but there are latent ACPI bugs/uncleanlinesses
where it references an already unmapped table. This worked by chance
until now, because we didnt actually unmap any tables - but now we
explicitly map/unmap the tables via the MMU. But, i dont think that's
the cause of the failure here - those bugs typically show up in other
ways.
> > that case it's a 64-bit early_ioremap() bug that we want to find
> > even if ACPI didnt use early_ioremap().
> >
> > and this all runs before zap_low_mappings(), right?
>
> No after. Since some time x86-64 does the equivalent of z_l_m() in
> head64(); this means before start_kernel and definitely before
> setup_arch which sets up ACPI.
that would mean early_ioremap() should switch to ioremap() after that
point. Could you try that, does it resolve the failure you are seeing?
Long-term we want to have a single, uniform ioremap() interface (on
32-bit and 64-bit x86 as well) that can be used anytime, which just
switches to the right lowlevel method depending on how far we are into
the pagetable and memory subsystem bootstrap - instead of these more
fragile "can we now use early_ioremap() or should we already be using
ioremap()" usages.
Ingo
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