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[Xen-devel] [PATCH V3 1/1] expand x86 arch_shared_info to support >3 level p2m tree

The x86 struct arch_shared_info field pfn_to_mfn_frame_list_list
currently contains the mfn of the top level page frame of the 3 level
p2m tree, which is used by the Xen tools during saving and restoring
(and live migration) of pv domains. With three levels of the p2m tree
it is possible to support up to 512 GB of RAM for a 64 bit pv domain.
A 32 bit pv domain can support more, as each memory page can hold 1024
instead of 512 entries, leading to a limit of 4 TB. To be able to
support more RAM on x86-64 an additional level is to be added.

This patch expands struct arch_shared_info with a new p2m tree root
and the number of levels of the p2m tree. The new information is
indicated by the domain to be valid by storing ~0UL into
pfn_to_mfn_frame_list_list (this should be done only if more than
three levels are needed, of course).

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
 xen/include/public/arch-x86/xen.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/xen/include/public/arch-x86/xen.h 
index f35804b..2ca996c 100644
--- a/xen/include/public/arch-x86/xen.h
+++ b/xen/include/public/arch-x86/xen.h
@@ -224,7 +224,12 @@ struct arch_shared_info {
     /* Frame containing list of mfns containing list of mfns containing p2m. */
     xen_pfn_t     pfn_to_mfn_frame_list_list;
     unsigned long nmi_reason;
-    uint64_t pad[32];
+    /*
+     * Following two fields are valid if pfn_to_mfn_frame_list_list contains
+     * ~0UL.
+     */
+    unsigned long p2m_levels;   /* number of levels of p2m tree */
+    xen_pfn_t     p2m_root;     /* p2m tree top level mfn */
 typedef struct arch_shared_info arch_shared_info_t;

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