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

Youquan Song committed 14 years ago

Commit 58a84aa1 parent b6999b12 files · +2 −1Browse files

Unified · Split

2 files

mm/hugetlb.c +1 −0
mm/page_alloc.c +1 −1

mm/hugetlb.c+1−0

@@ -576,6 +576,7 @@ static void prep_compound_gigantic_page(struct page *page, unsigned long order) · 575 unmodified lines
576	576	__SetPageHead(page);
577	577	for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
578	578	__SetPageTail(p);
	579	+ set_page_count(p, 0);
579	580	p->first_page = page;
580	581	}
581	582	}

mm/page_alloc.c+1−1

@@ -356,8 +356,8 @@ void prep_compound_page(struct page *page, unsigned long order) · 355 unmodified lines
356	356	__SetPageHead(page);
357	357	for (i = 1; i < nr_pages; i++) {
358	358	struct page *p = page + i;
359		−
360	359	__SetPageTail(p);
	360	+ set_page_count(p, 0);
361	361	p->first_page = page;
362	362	}
363	363	}