[Xen-devel] [for-4.7 2/2] xen/arm: p2m: Release the p2m lock before undoing the mappings

[Julien Grall <julien.grall@xxxxxxx>]

Since commit 4b25423a "arch/arm: unmap partially-mapped memory regions",
Xen has been undoing the P2M mappings when an error occurred during
insertion or memory allocation.

This is done by calling recursively apply_p2m_changes, however the
second call is done with the p2m lock taken which will result in a
deadlock for the current processor.

Fix it by moving the recursive call after the lock has been released.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

---
    I think we could unlock the p2m lock before freeing the temporary
    mapping. Although, I played safe as this is a bug fix for Xen 4.7
    and to be backported up to Xen 4.5.
---
 xen/arch/arm/p2m.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 68c67b0..838d004 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1184,6 +1184,14 @@ out:
     while ( (pg = page_list_remove_head(&free_pages)) )
         free_domheap_page(pg);
 
+    for ( level = P2M_ROOT_LEVEL; level < 4; level ++ )
+    {
+        if ( mappings[level] )
+            unmap_domain_page(mappings[level]);
+    }
+
+    spin_unlock(&p2m->lock);
+
     if ( rc < 0 && ( op == INSERT || op == ALLOCATE ) &&
          addr != start_gpaddr )
     {
@@ -1196,14 +1204,6 @@ out:
                           mattr, 0, p2m_invalid, d->arch.p2m.default_access);
     }
 
-    for ( level = P2M_ROOT_LEVEL; level < 4; level ++ )
-    {
-        if ( mappings[level] )
-            unmap_domain_page(mappings[level]);
-    }
-
-    spin_unlock(&p2m->lock);
-
     return rc;
 }
 
-- 
1.9.1


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