[PATCH] x86: fix PAE pmd_bad bootup warning
From: Hugh Dickins
Date: Tue May 06 2008 - 15:51:38 EST
Fix warning from pmd_bad() at bootup on a HIGHMEM64G HIGHPTE x86_32.
That came from 9fc34113f6880b215cbea4e7017fc818700384c2 x86: debug pmd_bad();
but we understand now that the typecasting was wrong for PAE in the previous
version: pagetable pages above 4GB looked bad and stopped Arjan from booting.
And revert that cded932b75ab0a5f9181ee3da34a0a488d1a14fd x86: fix pmd_bad
and pud_bad to support huge pages. It was the wrong way round: we shouldn't
weaken every pmd_bad and pud_bad check to let huge pages slip through - in
part they check that we _don't_ have a huge page where it's not expected.
Put the x86 pmd_bad() and pud_bad() definitions back to what they have long
been: they can be improved (x86_32 should use PTE_MASK, to stop PAE thinking
junk in the upper word is good; and x86_64 should follow x86_32's stricter
comparison, to stop thinking any subset of required bits is good); but that
should be a later patch.
Fix Hans' good observation that follow_page() will never find pmd_huge()
because that would have already failed the pmd_bad test: test pmd_huge in
between the pmd_none and pmd_bad tests. Tighten x86's pmd_huge() check?
No, once it's a hugepage entry, it can get quite far from a good pmd: for
example, PROT_NONE leaves it with only ACCESSED of the KERN_PGTABLE bits.
However... though follow_page() contains this and another test for huge
pages, so it's nice to keep it working on them, where does it actually get
called on a huge page? get_user_pages() checks is_vm_hugetlb_page(vma) to
to call alternative hugetlb processing, as does unmap_vmas() and others.
Signed-off-by: Hugh Dickins <hugh@xxxxxxxxxxx>
---
So Hans' original hugepage leak remains unexplained and unfixed.
Hans, did you find that hugepage leak with a standard kernel, or were
you perhaps trying out some hugepage-using patch of your own, without
marking the vma VM_HUGETLB? Or were you expecting the hugetlbfs file
to truncate itself once all mmappers had gone? If the standard kernel
leaks hugepages, I'm surprised the hugetlb guys don't know about it.
arch/x86/mm/pgtable_32.c | 7 -------
include/asm-x86/pgtable_32.h | 9 +--------
include/asm-x86/pgtable_64.h | 6 ++----
mm/memory.c | 5 ++++-
4 files changed, 7 insertions(+), 20 deletions(-)
--- 2.6.26-rc1/arch/x86/mm/pgtable_32.c 2008-05-03 21:54:41.000000000 +0100
+++ linux/arch/x86/mm/pgtable_32.c 2008-05-06 14:13:24.000000000 +0100
@@ -172,10 +172,3 @@ void reserve_top_address(unsigned long r
__FIXADDR_TOP = -reserve - PAGE_SIZE;
__VMALLOC_RESERVE += reserve;
}
-
-int pmd_bad(pmd_t pmd)
-{
- WARN_ON_ONCE(pmd_bad_v1(pmd) != pmd_bad_v2(pmd));
-
- return pmd_bad_v1(pmd);
-}
--- 2.6.26-rc1/include/asm-x86/pgtable_32.h 2008-05-03 21:55:10.000000000 +0100
+++ linux/include/asm-x86/pgtable_32.h 2008-05-06 14:13:24.000000000 +0100
@@ -88,14 +88,7 @@ extern unsigned long pg0[];
/* To avoid harmful races, pmd_none(x) should check only the lower when PAE */
#define pmd_none(x) (!(unsigned long)pmd_val((x)))
#define pmd_present(x) (pmd_val((x)) & _PAGE_PRESENT)
-
-extern int pmd_bad(pmd_t pmd);
-
-#define pmd_bad_v1(x) \
- (_KERNPG_TABLE != (pmd_val((x)) & ~(PAGE_MASK | _PAGE_USER)))
-#define pmd_bad_v2(x) \
- (_KERNPG_TABLE != (pmd_val((x)) & ~(PAGE_MASK | _PAGE_USER | \
- _PAGE_PSE | _PAGE_NX)))
+#define pmd_bad(x) ((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)
#define pages_to_mb(x) ((x) >> (20-PAGE_SHIFT))
--- 2.6.26-rc1/include/asm-x86/pgtable_64.h 2008-05-03 21:55:10.000000000 +0100
+++ linux/include/asm-x86/pgtable_64.h 2008-05-06 14:13:24.000000000 +0100
@@ -158,14 +158,12 @@ static inline unsigned long pgd_bad(pgd_
static inline unsigned long pud_bad(pud_t pud)
{
- return pud_val(pud) &
- ~(PTE_MASK | _KERNPG_TABLE | _PAGE_USER | _PAGE_PSE | _PAGE_NX);
+ return pud_val(pud) & ~(PTE_MASK | _KERNPG_TABLE | _PAGE_USER);
}
static inline unsigned long pmd_bad(pmd_t pmd)
{
- return pmd_val(pmd) &
- ~(PTE_MASK | _KERNPG_TABLE | _PAGE_USER | _PAGE_PSE | _PAGE_NX);
+ return pmd_val(pmd) & ~(PTE_MASK | _KERNPG_TABLE | _PAGE_USER);
}
#define pte_none(x) (!pte_val((x)))
--- 2.6.26-rc1/mm/memory.c 2008-05-03 21:55:12.000000000 +0100
+++ linux/mm/memory.c 2008-05-06 14:13:24.000000000 +0100
@@ -969,7 +969,7 @@ struct page *follow_page(struct vm_area_
goto no_page_table;
pmd = pmd_offset(pud, address);
- if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+ if (pmd_none(*pmd))
goto no_page_table;
if (pmd_huge(*pmd)) {
@@ -978,6 +978,9 @@ struct page *follow_page(struct vm_area_
goto out;
}
+ if (unlikely(pmd_bad(*pmd)))
+ goto no_page_table;
+
ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
if (!ptep)
goto out;
--
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