[Xen-devel] [PATCH] include/public: add new elf note for support of huge physical addresses

[Juergen Gross <jgross@xxxxxxxx>]

Current pv guests will only see physical addresses up to 46 bits wide.
In order to be able to run on a host supporting 5 level paging and to
make use of any possible memory page there, physical addresses with up
to 52 bits have to be supported.

As Xen needs to know whether a pv guest can handle such large addresses
the kernel of the guest has to advertise this capability.

Add a new ELF note for the maximum physical address the kernel can
make use of.

Please note that it is not required for a pv guest to support 5 level
paging in order to use high physical addresses.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
As I'd like to add support for large physical addresses in pv guests
rather sooner than later to the Linux kernel, I'm suggesting this
public interface change way before any 5 level paging support is added
to Xen.
---
 xen/include/public/elfnote.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/xen/include/public/elfnote.h b/xen/include/public/elfnote.h
index 936aa65822..8d76437f19 100644
--- a/xen/include/public/elfnote.h
+++ b/xen/include/public/elfnote.h
@@ -212,9 +212,18 @@
 #define XEN_ELFNOTE_PHYS32_ENTRY 18
 
 /*
+ * Maximum physical address size the kernel can handle.
+ *
+ * All memory of the PV guest must be allocated below this boundary,
+ * as the guest kernel can't handle page table entries with MFNs referring
+ * to memory above this value.
+ */
+#define XEN_ELFNOTE_MAXPHYS_SIZE 19
+
+/*
  * The number of the highest elfnote defined.
  */
-#define XEN_ELFNOTE_MAX XEN_ELFNOTE_PHYS32_ENTRY
+#define XEN_ELFNOTE_MAX XEN_ELFNOTE_MAXPHYS_SIZE
 
 /*
  * System information exported through crash notes.
-- 
2.12.3


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