libxc support of memory paging.

libxc accepts the new return code from privcmd mmap, which indicates a page
being mapped is actually paged out. Spin until the page is paged in and return
as normal to the caller. This allows memory paging to work transparently with
existing tools.

Since libxc runs in user-space, as does the pager, both processes will be
scheduled and run. This enables the page to be paged in without needing to
spin in kernel mode (which would cause a dead-lock).

Signed-off-by: Patrick Colp <Patrick.Colp@citrix.com>

1 files changed, 44 insertions, 1 deletions

diff --git a/tools/libxc/xc_linux.c b/tools/libxc/xc_linux.c
index 2d4a158af2..de176fbb8b 100644
--- a/tools/libxc/xc_linux.c
+++ b/tools/libxc/xc_linux.c
@@ -64,11 +64,34 @@ int xc_interface_close(int xc_handle)
     return close(xc_handle);
 }
 
+static int xc_map_foreign_batch_single(int xc_handle, uint32_t dom, int prot,
+                                       xen_pfn_t *mfn, unsigned long addr)
+{
+    privcmd_mmapbatch_t ioctlx;
+    int rc;
+
+    ioctlx.num = 1;
+    ioctlx.dom = dom;
+    ioctlx.addr = addr;
+    ioctlx.arr = mfn;
+
+    do
+    {
+        *mfn ^= XEN_DOMCTL_PFINFO_PAGEDTAB;
+        usleep(100);
+        rc = ioctl(xc_handle, IOCTL_PRIVCMD_MMAPBATCH, &ioctlx);
+    }
+    while ( (rc < 0) && (errno == ENOENT) );
+
+    return rc;
+}
+
 void *xc_map_foreign_batch(int xc_handle, uint32_t dom, int prot,
                            xen_pfn_t *arr, int num)
 {
     privcmd_mmapbatch_t ioctlx;
     void *addr;
+    int rc;
 
     addr = mmap(NULL, num << PAGE_SHIFT, prot, MAP_SHARED, xc_handle, 0);
     if ( addr == MAP_FAILED )
@@ -82,7 +105,27 @@ void *xc_map_foreign_batch(int xc_handle, uint32_t dom, int prot,
     ioctlx.addr = (unsigned long)addr;
     ioctlx.arr = arr;
 
-    if ( ioctl(xc_handle, IOCTL_PRIVCMD_MMAPBATCH, &ioctlx) < 0 )
+    rc = ioctl(xc_handle, IOCTL_PRIVCMD_MMAPBATCH, &ioctlx);
+    if ( (rc < 0) && (errno == ENOENT) )
+    {
+        int i;
+
+        for ( i = 0; i < num; i++ )
+        {
+            if ( (arr[i] & XEN_DOMCTL_PFINFO_LTAB_MASK) ==
+                 XEN_DOMCTL_PFINFO_PAGEDTAB )
+            {
+                unsigned long paged_addr = (unsigned long)addr + (i << PAGE_SHIFT);
+                rc = xc_map_foreign_batch_single(xc_handle, dom, prot, &arr[i],
+                                                 paged_addr);
+                if ( rc < 0 )
+                    goto out;
+            }
+        }
+    }
+
+ out:
+    if ( rc < 0 )
     {
         int saved_errno = errno;
         perror("xc_map_foreign_batch: ioctl failed");