[Xen-devel] [PATCH v3] xen: prevent PVH Dom0 from having pages with more than one ref

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

On PV guests a reference is taken when a page gets added to the page
tables, which makes pages added to the page tables have two
references, but this is not suitable for PVH that doesn't use the
PVMMU. In the PVH case only one reference has to be taken or else the
page would not be freed when the memory of the domain is decreased.

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
---
Changes since v2:
 - Reword commit message.
 - Add paging_mode_translate as a condition check to the already
   exiting gate in the second instance.

Changes since v1:
 - Fix coding style.
 - Fix a second occurrence of the same issue.
 - Use paging_mode_translate instead of is_pvh_domain.
---
 xen/arch/x86/domain_build.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/domain_build.c b/xen/arch/x86/domain_build.c
index ba42fc9..6666093 100644
--- a/xen/arch/x86/domain_build.c
+++ b/xen/arch/x86/domain_build.c
@@ -1137,10 +1137,13 @@ int __init construct_dom0(
                                     L1_PROT : COMPAT_L1_PROT));
         l1tab++;
 
-        page = mfn_to_page(mfn);
-        if ( (page->u.inuse.type_info == 0) &&
-             !get_page_and_type(page, d, PGT_writable_page) )
-            BUG();
+        if ( !paging_mode_translate(d) )
+        {
+            page = mfn_to_page(mfn);
+            if ( (page->u.inuse.type_info == 0) &&
+                 !get_page_and_type(page, d, PGT_writable_page) )
+                BUG();
+        }
     }
 
     if ( is_pv_32on64_domain(d) )
@@ -1300,7 +1303,7 @@ int __init construct_dom0(
         if ( get_gpfn_from_mfn(mfn) >= count )
         {
             BUG_ON(is_pv_32bit_domain(d));
-            if ( !page->u.inuse.type_info &&
+            if ( !paging_mode_translate(d) && !page->u.inuse.type_info &&
                  !get_page_and_type(page, d, PGT_writable_page) )
                 BUG();
 
-- 
1.7.7.5 (Apple Git-26)


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