[XEN PATCH v4 03/14] x86/p2m: guard altp2m routines

[Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>]

Initialize and bring down altp2m only when it is supported by the platform,
e.g. VMX. Also guard p2m_altp2m_propagate_change().
The purpose of that is the possibility to disable altp2m support and exclude its
code from the build completely, when it's not supported by the target platform.

Here hvm_altp2m_supported() is being used to check for ALTP2M availability,
which is only defined if HVM enabled, so a stub for that routine added for
!HVM configuration as well.

Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
---
New changes were made to patch after Jan reviewed it, namely 
hvm_altp2m_supported()
added for !HVM config, so I didn't put his Acked-by tag here.
---
changes in v4:
 - added stub for hvm_altp2m_supported() and description updated accordingly
changes in v3:
 - put hvm_altp2m_supported() first
 - rewrite changes to p2m_init() with less code
 - add tag
---
 xen/arch/x86/include/asm/hvm/hvm.h | 5 +++++
 xen/arch/x86/mm/p2m-basic.c        | 9 +++++----
 xen/arch/x86/mm/p2m-ept.c          | 2 +-
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/include/asm/hvm/hvm.h 
b/xen/arch/x86/include/asm/hvm/hvm.h
index 1c01e22c8e..277648dd18 100644
--- a/xen/arch/x86/include/asm/hvm/hvm.h
+++ b/xen/arch/x86/include/asm/hvm/hvm.h
@@ -828,6 +828,11 @@ static inline bool hvm_hap_supported(void)
     return false;
 }
 
+static inline bool hvm_altp2m_supported(void)
+{
+    return false;
+}
+
 static inline bool hvm_nested_virt_supported(void)
 {
     return false;
diff --git a/xen/arch/x86/mm/p2m-basic.c b/xen/arch/x86/mm/p2m-basic.c
index 25d27a0a9f..08007a687c 100644
--- a/xen/arch/x86/mm/p2m-basic.c
+++ b/xen/arch/x86/mm/p2m-basic.c
@@ -128,7 +128,7 @@ int p2m_init(struct domain *d)
         return rc;
     }
 
-    rc = p2m_init_altp2m(d);
+    rc = hvm_altp2m_supported() ? p2m_init_altp2m(d) : 0;
     if ( rc )
     {
         p2m_teardown_hostp2m(d);
@@ -197,11 +197,12 @@ void p2m_final_teardown(struct domain *d)
 {
     if ( is_hvm_domain(d) )
     {
+        if ( hvm_altp2m_supported() )
+            p2m_teardown_altp2m(d);
         /*
-         * We must tear down both of them unconditionally because
-         * we initialise them unconditionally.
+         * We must tear down nestedp2m unconditionally because
+         * we initialise it unconditionally.
          */
-        p2m_teardown_altp2m(d);
         p2m_teardown_nestedp2m(d);
     }
 
diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index 469e27ee93..49b76e9d16 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -991,7 +991,7 @@ out:
     if ( is_epte_present(&old_entry) )
         ept_free_entry(p2m, &old_entry, target);
 
-    if ( entry_written && p2m_is_hostp2m(p2m) )
+    if ( hvm_altp2m_supported() && entry_written && p2m_is_hostp2m(p2m) )
     {
         ret = p2m_altp2m_propagate_change(d, _gfn(gfn), mfn, order, p2mt, 
p2ma);
         if ( !rc )
-- 
2.25.1