xen: Mark all initial reserved pages for the balloon as INVALID_P2M_ENTRY.

With this patch, we diligently set regions that will be used by the
balloon driver to be INVALID_P2M_ENTRY and under the ownership
of the balloon driver. We are OK using the __set_phys_to_machine
as we do not expect to be allocating any P2M middle or entries pages.
The set_phys_to_machine has the side-effect of potentially allocating
new pages and we do not want that at this stage.

We can do this because xen_build_mfn_list_list will have already
allocated all such pages up to xen_max_p2m_pfn.

We also move the check for auto translated physmap down the
stack so it is present in __set_phys_to_machine.

[v2: Rebased with mmu->p2m code split]
Reviewed-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 4 insertions, 5 deletions

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index ddc81a06edb9..df4e36775339 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -365,6 +365,10 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 {
         unsigned topidx, mididx, idx;
 
+        if (unlikely(xen_feature(XENFEAT_auto_translated_physmap))) {
+                BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
+                return true;
+        }
         if (unlikely(pfn >= MAX_P2M_PFN)) {
                 BUG_ON(mfn != INVALID_P2M_ENTRY);
                 return true;
@@ -384,11 +388,6 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 
 bool set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 {
-        if (unlikely(xen_feature(XENFEAT_auto_translated_physmap))) {
-                BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
-                return true;
-        }
-
         if (unlikely(!__set_phys_to_machine(pfn, mfn)))  {
                 if (!alloc_p2m(pfn))
                         return false;