Use a reserved pfn in the guest address space to store mem event rings

This solves a long-standing issue in which the pages backing these rings were
pages belonging to dom0 user-space processes. Thus, if the process would die
unexpectedly, Xen would keep posting events to a page now belonging to some
other process.

We update all API-consumers in tree (xenpaging and xen-access).

This is an API/ABI change, so please speak up if it breaks your accumptions.

The patch touches tools, hypervisor x86/hvm bits, and hypervisor x86/mm bits.

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Acked-by: Tim Deegan <tim@xen.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Tim Deegan <tim@xen.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/tools/libxc/xc_domain_save.c b/tools/libxc/xc_domain_save.c
index 9fa39b2f1c..a9216ddf71 100644
--- a/tools/libxc/xc_domain_save.c
+++ b/tools/libxc/xc_domain_save.c
@@ -1639,6 +1639,42 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
             goto out;
         }
 
+        chunk.id = XC_SAVE_ID_HVM_PAGING_RING_PFN;
+        chunk.data = 0;
+        xc_get_hvm_param(xch, dom, HVM_PARAM_PAGING_RING_PFN,
+                         (unsigned long *)&chunk.data);
+
+        if ( (chunk.data != 0) &&
+             wrexact(io_fd, &chunk, sizeof(chunk)) )
+        {
+            PERROR("Error when writing the paging ring pfn for guest");
+            goto out;
+        }
+
+        chunk.id = XC_SAVE_ID_HVM_ACCESS_RING_PFN;
+        chunk.data = 0;
+        xc_get_hvm_param(xch, dom, HVM_PARAM_ACCESS_RING_PFN,
+                         (unsigned long *)&chunk.data);
+
+        if ( (chunk.data != 0) &&
+             wrexact(io_fd, &chunk, sizeof(chunk)) )
+        {
+            PERROR("Error when writing the access ring pfn for guest");
+            goto out;
+        }
+
+        chunk.id = XC_SAVE_ID_HVM_SHARING_RING_PFN;
+        chunk.data = 0;
+        xc_get_hvm_param(xch, dom, HVM_PARAM_SHARING_RING_PFN,
+                         (unsigned long *)&chunk.data);
+
+        if ( (chunk.data != 0) &&
+             wrexact(io_fd, &chunk, sizeof(chunk)) )
+        {
+            PERROR("Error when writing the sharing ring pfn for guest");
+            goto out;
+        }
+
         chunk.id = XC_SAVE_ID_HVM_VM86_TSS;
         chunk.data = 0;
         xc_get_hvm_param(xch, dom, HVM_PARAM_VM86_TSS,