[Xen-devel] [PATCH] vm_event: Fix regression caused by b701ccc8

[Tamas K Lengyel <tlengyel@xxxxxxxxxxx>]

When xc_map_foreign_batch got deprecated reinitializing vm_event on a domain
where an event listener was previously active broke as it relied on the flag
XEN_DOMCTL_PFINFO_XTAB to indicate that the magic page is not in the physmap.
Manually check the gpfn type, add it to the physmap if needed, and only then
try to map it.

Signed-off-by: Tamas K Lengyel <tlengyel@xxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 tools/libxc/xc_vm_event.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/tools/libxc/xc_vm_event.c b/tools/libxc/xc_vm_event.c
index 57abce0..443c73b 100644
--- a/tools/libxc/xc_vm_event.c
+++ b/tools/libxc/xc_vm_event.c
@@ -72,11 +72,10 @@ void *xc_vm_event_enable(xc_interface *xch, domid_t 
domain_id, int param,
 
     ring_pfn = pfn;
     mmap_pfn = pfn;
-    ring_page = xc_map_foreign_pages(xch, domain_id, PROT_READ | PROT_WRITE,
-                                     &mmap_pfn, 1);
-    if ( !ring_page )
+    rc1 = xc_get_pfn_type_batch(xch, domain_id, 1, &mmap_pfn);
+    if ( rc1 || mmap_pfn & XEN_DOMCTL_PFINFO_XTAB )
     {
-        /* Map failed, populate ring page */
+        /* Page not in the physmap, try to populate it */
         rc1 = xc_domain_populate_physmap_exact(xch, domain_id, 1, 0, 0,
                                               &ring_pfn);
         if ( rc1 != 0 )
@@ -84,15 +83,15 @@ void *xc_vm_event_enable(xc_interface *xch, domid_t 
domain_id, int param,
             PERROR("Failed to populate ring pfn\n");
             goto out;
         }
+    }
 
-        mmap_pfn = ring_pfn;
-        ring_page = xc_map_foreign_pages(xch, domain_id, PROT_READ | 
PROT_WRITE,
+    mmap_pfn = ring_pfn;
+    ring_page = xc_map_foreign_pages(xch, domain_id, PROT_READ | PROT_WRITE,
                                          &mmap_pfn, 1);
-        if ( !ring_page )
-        {
-            PERROR("Could not map the ring page\n");
-            goto out;
-        }
+    if ( !ring_page )
+    {
+        PERROR("Could not map the ring page\n");
+        goto out;
     }
 
     switch ( param )
-- 
2.1.4


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