Re: early fixmap causes kmap breakage

[Nick Piggin]

On Tue, Dec 30, 2008 at 07:13:44AM +0100, Ingo Molnar wrote:
> 
> * Nick Piggin <npiggin@xxxxxxx> 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@xxxxxxx> 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);
+				newpte = one_page_table_init(pmd);
+				BUG_ON(lastpte + PTRS_PER_PTE != newpte);
+				memset(newpte, pte, PAGE_SIZE);
+				pte = lastpte;
+			}
+			lastpte = pte;
 
 			vaddr += PMD_SIZE;
 		}
--
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