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Commit c283610e authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
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x86, mm: do not leak page->ptl for pmd page tables 



There are two code paths how page with pmd page table can be freed:
pmd_free() and pmd_free_tlb().

I've missed the second one and didn't add page table destructor call
there.  It leads to leak of page->ptl for pmd page tables, if
dynamically allocated page->ptl is in use.

The patch adds the missed destructor and modifies documentation
accordingly.

Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: default avatarAndrey Vagin <avagin@openvz.org>
Tested-by: default avatarAndrey Vagin <avagin@openvz.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3a72660b

Documentation/vm/split_page_table_lock

+3 −3
Original line number Diff line number Diff line
@@ -63,9 +63,9 @@ levels. 
PMD split lock enabling requires pgtable_pmd_page_ctor() call on PMD table

allocation and pgtable_pmd_page_dtor() on freeing.



Allocation usually happens in pmd_alloc_one(), freeing in pmd_free(), but

make sure you cover all PMD table allocation / freeing paths: i.e X86_PAE

preallocate few PMDs on pgd_alloc().

Allocation usually happens in pmd_alloc_one(), freeing in pmd_free() and

pmd_free_tlb(), but make sure you cover all PMD table allocation / freeing

paths: i.e X86_PAE preallocate few PMDs on pgd_alloc().



With everything in place you can set CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK.

arch/x86/mm/pgtable.c

+3 −1
Original line number Diff line number Diff line
@@ -61,6 +61,7 @@ void ___pte_free_tlb(struct mmu_gather *tlb, struct page *pte) 
#if PAGETABLE_LEVELS > 2

void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)

{

	struct page *page = virt_to_page(pmd);

	paravirt_release_pmd(__pa(pmd) >> PAGE_SHIFT);

	/*

	 * NOTE! For PAE, any changes to the top page-directory-pointer-table
@@ -69,7 +70,8 @@ void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd) 
#ifdef CONFIG_X86_PAE

	tlb->need_flush_all = 1;

#endif

	tlb_remove_page(tlb, virt_to_page(pmd));

	pgtable_pmd_page_dtor(page);

	tlb_remove_page(tlb, page);

}



#if PAGETABLE_LEVELS > 3