xen: add m2p override mechanism

Add a simple hashtable based mechanism to override some portions of the
m2p, so that we can find out the pfn corresponding to an mfn of a
granted page. In fact entries corresponding to granted pages in the m2p
hold the original pfn value of the page in the source domain that
granted it.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 13 insertions, 3 deletions

diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index 8760cc60a21c..50f0a0f6bd6a 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -42,6 +42,11 @@ extern unsigned int   machine_to_phys_order;
 extern unsigned long get_phys_to_machine(unsigned long pfn);
 extern bool set_phys_to_machine(unsigned long pfn, unsigned long mfn);
 
+extern void m2p_add_override(unsigned long mfn, struct page *page);
+extern void m2p_remove_override(struct page *page);
+extern struct page *m2p_find_override(unsigned long mfn);
+extern unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn);
+
 static inline unsigned long pfn_to_mfn(unsigned long pfn)
 {
         unsigned long mfn;
@@ -72,9 +77,6 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
         if (xen_feature(XENFEAT_auto_translated_physmap))
                 return mfn;
 
-        if (unlikely((mfn >> machine_to_phys_order) != 0))
-                return ~0;
-
         pfn = 0;
         /*
          * The array access can fail (e.g., device space beyond end of RAM).
@@ -83,6 +85,14 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
          */
         __get_user(pfn, &machine_to_phys_mapping[mfn]);
 
+        /*
+         * If this appears to be a foreign mfn (because the pfn
+         * doesn't map back to the mfn), then check the local override
+         * table to see if there's a better pfn to use.
+         */
+        if (get_phys_to_machine(pfn) != mfn)
+                pfn = m2p_find_override_pfn(mfn, pfn);
+
         return pfn;
 }