xen p2m: transparently change the p2m mappings in the m2p override

In m2p_add_override store the original mfn into page->index and then
change the p2m mapping, setting mfns as FOREIGN_FRAME.

In m2p_remove_override restore the original mapping.

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

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 8db19d50c467..b3b19d43b951 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -407,8 +407,11 @@ static unsigned long mfn_hash(unsigned long mfn)
 void m2p_add_override(unsigned long mfn, struct page *page)
 {
         unsigned long flags;
+        unsigned long pfn = page_to_pfn(page);
         page->private = mfn;
+        page->index = pfn_to_mfn(pfn);
 
+        __set_phys_to_machine(pfn, FOREIGN_FRAME(mfn));
         spin_lock_irqsave(&m2p_override_lock, flags);
         list_add(&page->lru,  &m2p_overrides[mfn_hash(mfn)]);
         spin_unlock_irqrestore(&m2p_override_lock, flags);
@@ -417,9 +420,18 @@ void m2p_add_override(unsigned long mfn, struct page *page)
 void m2p_remove_override(struct page *page)
 {
         unsigned long flags;
+        unsigned long mfn;
+        unsigned long pfn;
+
+        pfn = page_to_pfn(page);
+        mfn = get_phys_to_machine(pfn);
+        if (mfn == INVALID_P2M_ENTRY || !(mfn & FOREIGN_FRAME_BIT))
+                return;
+
         spin_lock_irqsave(&m2p_override_lock, flags);
         list_del(&page->lru);
         spin_unlock_irqrestore(&m2p_override_lock, flags);
+        __set_phys_to_machine(pfn, page->index);
 }
 
 struct page *m2p_find_override(unsigned long mfn)