[Xen-devel] [PATCH] x86/mem_sharing: Rectify test for "empty" physmap entry in sharing_add_to_physmap

[Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>]

 xen/arch/x86/mm/mem_sharing.c |  6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)


Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>

diff -r 8609bbbba141 -r 495d3df95c1d xen/arch/x86/mm/mem_sharing.c
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1073,9 +1073,11 @@ int mem_sharing_add_to_physmap(struct do
     if ( spage->sharing->handle != sh )
         goto err_unlock;
 
-    /* Make sure the target page is a hole in the physmap */
+    /* Make sure the target page is a hole in the physmap. This is not as
+     * simple a test as we'd like it to be. Non-existent p2m entries return
+     * invalid mfn and p2m_mmio_dm type when queried. */
     if ( mfn_valid(cmfn) ||
-         (!(p2m_is_ram(cmfn_type))) )
+         ( (!(p2m_is_ram(cmfn_type))) && (cmfn_type != p2m_mmio_dm) ) )
     {
         ret = XENMEM_SHARING_OP_C_HANDLE_INVALID;
         goto err_unlock;

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