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authorAndrea Arcangeli <aarcange@redhat.com>2011-01-13 15:46:48 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-01-13 17:32:41 -0800
commit936a5fe6e6148c0b3ea0d792b903847d9b9931a1 (patch)
treef0326a5877a89251ff2cb727d5e832e911ed1d18 /virt
parent47ad8475c000141eacb3ecda5e5ce4b43a9cd04d (diff)
downloadlinux-936a5fe6e6148c0b3ea0d792b903847d9b9931a1.tar.gz
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>
Diffstat (limited to 'virt')
-rw-r--r--virt/kvm/kvm_main.c32
1 files changed, 30 insertions, 2 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 7f686251f71..85ab7db0d36 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;