1 files changed, 13 insertions, 0 deletions

diff --git a/arch/i386/xen/mmu.h b/arch/i386/xen/mmu.h
index 49776fe9f02a..c9ff27f3ac3a 100644
--- a/arch/i386/xen/mmu.h
+++ b/arch/i386/xen/mmu.h
@@ -3,6 +3,19 @@
 #include <linux/linkage.h>
 #include <asm/page.h>
 
+/*
+ * Page-directory addresses above 4GB do not fit into architectural %cr3.
+ * When accessing %cr3, or equivalent field in vcpu_guest_context, guests
+ * must use the following accessor macros to pack/unpack valid MFNs.
+ *
+ * Note that Xen is using the fact that the pagetable base is always
+ * page-aligned, and putting the 12 MSB of the address into the 12 LSB
+ * of cr3.
+ */
+#define xen_pfn_to_cr3(pfn) (((unsigned)(pfn) << 12) | ((unsigned)(pfn) >> 20))
+#define xen_cr3_to_pfn(cr3) (((unsigned)(cr3) >> 12) | ((unsigned)(cr3) << 20))
+
+
 void set_pte_mfn(unsigned long vaddr, unsigned long pfn, pgprot_t flags);
 
 void xen_set_pte(pte_t *ptep, pte_t pteval);