From 58a84aa92723d1ac3e1cc4e3b0ff49291663f7e1 Mon Sep 17 00:00:00 2001 From: Youquan Song Date: Thu, 8 Dec 2011 14:34:18 -0800 Subject: [PATCH] thp: set compound tail page _count to zero Commit 70b50f94f1644 ("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 Reviewed-by: Andrea Arcangeli Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hugetlb.c | 1 + mm/page_alloc.c | 2 +- 2 files changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index bb28a5f9db8d..73f17c0293c0 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -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; } } diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9dd443d89d8b..850009a7101e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -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; } } -- 2.20.1