Messages in this thread | | | Date | Sun, 20 Jan 2008 18:59:55 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] Fix early_ioremap on x86-64 |
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* Andi Kleen <andi@firstfloor.org> wrote:
> Fix early_ioremap on x86-64 > > [Venki, sorry for blaming PAT for this earlier. It was innocent.] > [Note the patch is on top of git-x86 + gbpages applied. I think there > will be an trivial reject without gbpages-direct applied first] > > I had ACPI failures on several machines since a few days. Symptom was > NUMA nodes not getting detected or worse cores not getting detected. > They all came from ACPI not being able to read various of its tables. > I finally bisected it down to Jeremy's "put _PAGE_GLOBAL into > PAGE_KERNEL" change. With that the fix was fairly obvious. The problem > was that early_ioremap() didn't use a "_all" flush that would affect > the global PTEs too. So with global bits getting used everywhere now > an early_ioremap would not actually flush a mapping if something else > was mapped previously on that slot (which can happen with > early_iounmap inbetween) > > This patch changes all flushes in init_64.c to be __flush_tlb_all() > and fixes the problem here.
ah, very nice! This is the bad commit:
-------------------------> Subject: x86: fold _PAGE_GLOBAL into __PAGE_KERNEL From: Jeremy Fitzhardinge <jeremy@goop.org>
With the iounmap problem resolved, it should be OK to always set _PAGE_GLOBAL in __PAGE_KERNEL*.
[ Did this patch cause problems before? ] <------------------------
Jeremy did suspect something about this change, as indicated in the changelog. But because the change was so finegrained, the bisection almost directly led to the fix. _That_ i think clearly demonstrates the power of bisection and finegrained changes.
but note what the fundamental problem is - we've turned a previously safe flushing API into an unsafe one - __flush_tlb() will only be safe in the rarest of circumstances. There are some other matches:
./mm/init_64.c: __flush_tlb(); ./kernel/head64.c: __flush_tlb();
The boot identity mappings zapped do not have PGE set at the moment, but they could in the future (once we do native pagetable setup straight from flat mode) - and this is not a performance critical path anyway.
./kernel/cpu/mtrr/generic.c: __flush_tlb(); ./kernel/cpu/mtrr/generic.c: __flush_tlb();
these include an open-coded version of __flush_tlb_all() so they are safe.
and we might as well make the non-PGE flush the 'special API'. I.e. rename __flush_tlb() to __flush_tlb_partial() and rename __flush_tlb_all() to __flush_tlb(). This makes it very apparent which should be used by default and which does what.
Ingo
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