diff options
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/kvm_main.c | 32 |
1 files changed, 30 insertions, 2 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7f68625..85ab7db 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -104,8 +104,36 @@ static pfn_t fault_pfn; inline int kvm_is_mmio_pfn(pfn_t pfn) { if (pfn_valid(pfn)) { - struct page *page = compound_head(pfn_to_page(pfn)); - return PageReserved(page); + struct page *head; + struct page *tail = pfn_to_page(pfn); + head = compound_head(tail); + if (head != tail) { + smp_rmb(); + /* + * head may be a dangling pointer. + * __split_huge_page_refcount clears PageTail + * before overwriting first_page, so if + * PageTail is still there it means the head + * pointer isn't dangling. + */ + if (PageTail(tail)) { + /* + * the "head" is not a dangling + * pointer but the hugepage may have + * been splitted from under us (and we + * may not hold a reference count on + * the head page so it can be reused + * before we run PageReferenced), so + * we've to recheck PageTail before + * returning what we just read. + */ + int reserved = PageReserved(head); + smp_rmb(); + if (PageTail(tail)) + return reserved; + } + } + return PageReserved(tail); } return true; |