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    SubjectRe: early fixmap causes kmap breakage
    On Tue, Dec 30, 2008 at 08:54:28AM +0100, Nick Piggin wrote:
    > On Tue, Dec 30, 2008 at 07:13:44AM +0100, Ingo Molnar wrote:
    > >
    > > * Nick Piggin <npiggin@suse.de> wrote:
    > >
    > > > On Mon, Dec 29, 2008 at 03:17:31PM -0800, Andrew Morton wrote:
    > > > > On Thu, 18 Dec 2008 22:15:43 +0100
    > > > > Nick Piggin <npiggin@suse.de> wrote:
    > > > >
    > > > > > Hi,
    > > > > >
    > > > > > I've debugged a problem where i386+pae systems with more than a few CPUs
    > > > > > blow up at boot in the kmap_atomic code.
    > > > >
    > > > > ping?
    > > >
    > > > No further progress here, I'm waiting on input for how to fix this
    > > > "nicely". Meantime, clearing the early fixmap pte I guess works, but you
    > > > lose a page... is it possible to put it into .initdata or is there some
    > > > issue with that? (I guess on a PAE kernel, 4K isn't a big deal).
    > >
    > > yeah, 4K shouldnt be a big deal. Mind sending a patch for this?
    >
    > I don't know if we should put a warning when we encounter this condition,
    > to help catch other unintended uses...
    >
    > But this at least clears out the early fixmap pte and provides a contiguous
    > allocation...
    >
    > ---
    > arch/x86/mm/init_32.c | 15 ++++++++++++++-
    > 1 file changed, 14 insertions(+), 1 deletion(-)
    >
    > Index: linux-2.6/arch/x86/mm/init_32.c
    > ===================================================================
    > --- linux-2.6.orig/arch/x86/mm/init_32.c
    > +++ linux-2.6/arch/x86/mm/init_32.c
    > @@ -155,6 +155,7 @@ page_table_range_init(unsigned long star
    > unsigned long vaddr;
    > pgd_t *pgd;
    > pmd_t *pmd;
    > + pte_t *lastpte = NULL;
    >
    > vaddr = start;
    > pgd_idx = pgd_index(vaddr);
    > @@ -166,7 +167,19 @@ page_table_range_init(unsigned long star
    > pmd = pmd + pmd_index(vaddr);
    > for (; (pmd_idx < PTRS_PER_PMD) && (vaddr != end);
    > pmd++, pmd_idx++) {
    > - one_page_table_init(pmd);
    > + pte_t *pte;
    > +
    > + pte = one_page_table_init(pmd);
    > + if (lastpte && lastpte + PTRS_PER_PTE != pte) {
    > + pte_t *newpte;
    > +
    > + pmd_clear(pmd);

    Hmm, no actually we do need a TLB flush here.

    > + newpte = one_page_table_init(pmd);
    > + BUG_ON(lastpte + PTRS_PER_PTE != newpte);
    > + memset(newpte, pte, PAGE_SIZE);

    And here we probably need a loop doing set_pte just in case the
    CPU speculatively loads an incomplete TLB...

    > + pte = lastpte;
    > + }
    > + lastpte = pte;
    >
    > vaddr += PMD_SIZE;
    > }


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