Messages in this thread | | | Date | Sat, 19 Jan 2008 16:30:55 +0100 | From | Ingo Molnar <> | Subject | Re: ACPI early ioremap problems |
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(Cc:-ing to lkml, because this might interest others too)
* Andi Kleen <andi@firstfloor.org> 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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