[Xen-devel] [PATCH 1/4] expand x86 arch_shared_info to support linear p2m list

[Juergen Gross <jgross@xxxxxxxx>]

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 and for crash dump analysis. 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 switch to a virtual mapped
p2m list.

This patch expands struct arch_shared_info with a new p2m list virtual
address and the mfn of the page table root. The new information is
indicated by the domain to be valid by storing ~0UL into
pfn_to_mfn_frame_list_list. The hypervisor indicates usability of this
feature by a new flag XENFEAT_virtual_p2m.
---
 xen/include/public/arch-x86/xen.h | 7 ++++++-
 xen/include/public/features.h     | 3 +++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/xen/include/public/arch-x86/xen.h 
b/xen/include/public/arch-x86/xen.h
index f35804b..b0f85a9 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_vaddr;    /* virtual address of the p2m list */
+    unsigned long p2m_as_root;  /* mfn of the top level page table */
 };
 typedef struct arch_shared_info arch_shared_info_t;
 
diff --git a/xen/include/public/features.h b/xen/include/public/features.h
index 16d92aa..ff0b82d 100644
--- a/xen/include/public/features.h
+++ b/xen/include/public/features.h
@@ -99,6 +99,9 @@
 #define XENFEAT_grant_map_identity        12
  */
 
+/* x86: guest may specify virtual address of p2m list */
+#define XENFEAT_virtual_p2m               13
+
 #define XENFEAT_NR_SUBMAPS 1
 
 #endif /* __XEN_PUBLIC_FEATURES_H__ */
-- 
2.1.2


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