thp: kvm mmu transparent hugepage support
This should work for both hugetlbfs and transparent hugepages.
[akpm@linux-foundation.org: bring forward PageTransCompound() addition for bisectability]
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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 @@
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;