[PATCH 7/8] docs: Document start_info changes in Xen 4.2.

[Konrad Rzeszutek Wilk <konrad@kernel.org>]

The git commit 7a9d7646307b7c872b8dbd7546579acd3b54223d "x86/32-on-64:
adjust Dom0 initial page table layout" fixes a bug in the reported
value of pt_base versus what is stored in the %cr3 register. This
documents this in the start of the world header note.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 xen/include/public/xen.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
index c50bbfc..1685317 100644
--- a/xen/include/public/xen.h
+++ b/xen/include/public/xen.h
@@ -705,6 +705,13 @@ typedef struct shared_info shared_info_t;
  *  8. There is guaranteed to be at least 512kB padding after the final
  *     bootstrap element. If necessary, the bootstrap virtual region is
  *     extended by an extra 4MB to ensure this.
+ *
+ * Note: Prior to 7a9d7646307b7c872b8dbd7546579acd3b54223d ("x86/32-on-64:
+ * adjust Dom0 initial page table layout") the 3.e) contained two different
+ * values with a 64-bit hypervisor and a 32-bit initial domain kernel. The
+ * pt_base pointed to the L4 (setup by the hypervisor and not used by
+ * the guest) and the %cr3 pointed to the L3. This meant an difference of
+ * one page.
  */
 
 #define MAX_GUEST_CMDLINE 1024
-- 
1.7.11.7