3 files changed, 38 insertions, 2 deletions

diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index e7d05900efac..d88bfd66aaab 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -53,6 +53,6 @@ config XEN_DEBUG_FS
 
 config XEN_PVH
         bool "Support for running as a PVH guest"
-        depends on X86_64 && XEN && BROKEN
+        depends on X86_64 && XEN
         select XEN_PVHVM
         def_bool n
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 7faed5869e5b..485b69585540 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -11,8 +11,28 @@
 #include <asm/page_types.h>
 
 #include <xen/interface/elfnote.h>
+#include <xen/interface/features.h>
 #include <asm/xen/interface.h>
 
+#ifdef CONFIG_XEN_PVH
+#define PVH_FEATURES_STR  "|writable_descriptor_tables|auto_translated_physmap|supervisor_mode_kernel"
+/* Note the lack of 'hvm_callback_vector'. Older hypervisor will
+ * balk at this being part of XEN_ELFNOTE_FEATURES, so we put it in
+ * XEN_ELFNOTE_SUPPORTED_FEATURES which older hypervisors will ignore.
+ */
+#define PVH_FEATURES ((1 << XENFEAT_writable_page_tables) | \
+                      (1 << XENFEAT_auto_translated_physmap) | \
+                      (1 << XENFEAT_supervisor_mode_kernel) | \
+                      (1 << XENFEAT_hvm_callback_vector))
+/* The XENFEAT_writable_page_tables is not stricly neccessary as we set that
+ * up regardless whether this CONFIG option is enabled or not, but it
+ * clarifies what the right flags need to be.
+ */
+#else
+#define PVH_FEATURES_STR  ""
+#define PVH_FEATURES (0)
+#endif
+
         __INIT
 ENTRY(startup_xen)
         cld
@@ -95,7 +115,10 @@ NEXT_HYPERCALL(arch_6)
 #endif
         ELFNOTE(Xen, XEN_ELFNOTE_ENTRY,          _ASM_PTR startup_xen)
         ELFNOTE(Xen, XEN_ELFNOTE_HYPERCALL_PAGE, _ASM_PTR hypercall_page)
-        ELFNOTE(Xen, XEN_ELFNOTE_FEATURES,       .asciz "!writable_page_tables|pae_pgdir_above_4gb")
+        ELFNOTE(Xen, XEN_ELFNOTE_FEATURES,       .ascii "!writable_page_tables|pae_pgdir_above_4gb"; .asciz PVH_FEATURES_STR)
+        ELFNOTE(Xen, XEN_ELFNOTE_SUPPORTED_FEATURES, .long (PVH_FEATURES) |
+                                                (1 << XENFEAT_writable_page_tables) |
+                                                (1 << XENFEAT_dom0))
         ELFNOTE(Xen, XEN_ELFNOTE_PAE_MODE,       .asciz "yes")
         ELFNOTE(Xen, XEN_ELFNOTE_LOADER,         .asciz "generic")
         ELFNOTE(Xen, XEN_ELFNOTE_L1_MFN_VALID,
diff --git a/include/xen/interface/elfnote.h b/include/xen/interface/elfnote.h
index 0360b15f4883..6f4eae328ca7 100644
--- a/include/xen/interface/elfnote.h
+++ b/include/xen/interface/elfnote.h
@@ -140,6 +140,19 @@
  */
 #define XEN_ELFNOTE_SUSPEND_CANCEL 14
 
+/*
+ * The features supported by this kernel (numeric).
+ *
+ * Other than XEN_ELFNOTE_FEATURES on pre-4.2 Xen, this note allows a
+ * kernel to specify support for features that older hypervisors don't
+ * know about. The set of features 4.2 and newer hypervisors will
+ * consider supported by the kernel is the combination of the sets
+ * specified through this and the string note.
+ *
+ * LEGACY: FEATURES
+ */
+#define XEN_ELFNOTE_SUPPORTED_FEATURES 17
+
 #endif /* __XEN_PUBLIC_ELFNOTE_H__ */
 
 /*