Commit 58a84aa9 authored Dec 08, 2011 by Youquan Song Committed by Linus Torvalds Dec 09, 2011

thp: set compound tail page _count to zero



Commit 70b50f94 ("mm: thp: tail page refcounting fix") keeps all
page_tail->_count zero at all times.  But the current kernel does not
set page_tail->_count to zero if a 1GB page is utilized.  So when an
IOMMU 1GB page is used by KVM, it wil result in a kernel oops because a
tail page's _count does not equal zero.

  kernel BUG at include/linux/mm.h:386!
  invalid opcode: 0000 [#1] SMP
  Call Trace:
    gup_pud_range+0xb8/0x19d
    get_user_pages_fast+0xcb/0x192
    ? trace_hardirqs_off+0xd/0xf
    hva_to_pfn+0x119/0x2f2
    gfn_to_pfn_memslot+0x2c/0x2e
    kvm_iommu_map_pages+0xfd/0x1c1
    kvm_iommu_map_memslots+0x7c/0xbd
    kvm_iommu_map_guest+0xaa/0xbf
    kvm_vm_ioctl_assigned_device+0x2ef/0xa47
    kvm_vm_ioctl+0x36c/0x3a2
    do_vfs_ioctl+0x49e/0x4e4
    sys_ioctl+0x5a/0x7c
    system_call_fastpath+0x16/0x1b
  RIP  gup_huge_pud+0xf2/0x159

Signed-off-by: Youquan Song <youquan.song@intel.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent b6999b19

mm/hugetlb.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -576,6 +576,7 @@ static void prep_compound_gigantic_page(struct page *page, unsigned long order)
		__SetPageHead(page);
		for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
		__SetPageTail(p);
		set_page_count(p, 0);
		p->first_page = page;
		}
		}

mm/page_alloc.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -356,8 +356,8 @@ void prep_compound_page(struct page *page, unsigned long order)
		__SetPageHead(page);
		for (i = 1; i < nr_pages; i++) {
		struct page *p = page + i;

		__SetPageTail(p);
		set_page_count(p, 0);
		p->first_page = page;
		}
		}

Admin message