[Xen-devel] [PATCH] x86/mm: early put_page when XENMEM_add_to_physmap(XENMAPSPACE_gmfn)

[Kouya Shimura <kouya@xxxxxxxxxxxxxx>]

When using a stub domain, xen massively complains as follows:

(XEN) sh error: sh_remove_all_mappings(): can't find all mappings of mfn be3c5: 
c=8000000000000004 t=00000000
(XEN) sh error: sh_remove_all_mappings(): can't find all mappings of mfn be3c4: 
c=8000000000000004 t=00000000
...

This comes from the XENMEM_add_to_physmap hypercall from hvmloader.

The guest_physmap_remove_page function calls sh_remove_all_mappings()
which checks reference count of the page. Then, calling
guest_physmap_remove_page after temporarily get_page is obviously
wrong. And early put_page is harmless here since domain_lock is
acquired.

Also, the restore program seems not to complain extra mappings
long before. Instead, the stub domain does. Thus the comment in
sh_remove_all_mappings() is rewritten.


Signed-off-by: Kouya Shimura <kouya@xxxxxxxxxxxxxx>

diff -r 07f98beddc18 xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c Wed Dec 23 08:22:13 2009 +0000
+++ b/xen/arch/x86/mm.c Thu Dec 24 14:07:04 2009 +0900
@@ -4304,6 +4304,9 @@ long arch_memory_op(int op, XEN_GUEST_HA
 
         domain_lock(d);
 
+        if ( page )
+            put_page(page);
+
         /* Remove previously mapped page if it was present. */
         prev_mfn = gmfn_to_mfn(d, xatp.gpfn);
         if ( mfn_valid(prev_mfn) )
@@ -4326,9 +4329,6 @@ long arch_memory_op(int op, XEN_GUEST_HA
         rc = guest_physmap_add_page(d, xatp.gpfn, mfn, 0);
 
         domain_unlock(d);
-
-        if ( page )
-            put_page(page);
 
         rcu_unlock_domain(d);
 
diff -r 07f98beddc18 xen/arch/x86/mm/shadow/common.c
--- a/xen/arch/x86/mm/shadow/common.c   Wed Dec 23 08:22:13 2009 +0000
+++ b/xen/arch/x86/mm/shadow/common.c   Thu Dec 24 14:07:04 2009 +0900
@@ -2606,7 +2606,7 @@ int sh_remove_all_mappings(struct vcpu *
     {
         /* Don't complain if we're in HVM and there are some extra mappings: 
          * The qemu helper process has an untyped mapping of this dom's RAM 
-         * and the HVM restore program takes another. */
+         * and the stub domain takes another. */
         if ( !(shadow_mode_external(v->domain)
                && (page->count_info & PGC_count_mask) <= 3
                && (page->u.inuse.type_info & PGT_count_mask) == 0) )

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