commit f86a7a837207a1260ff7a8e4469b9057fbde11c8
Author: Jim Fehlig <jfehlig@suse.com>
Date:   Tue Jan 17 15:11:32 2017 -0700

    libxl: fix dom0 autoballooning with Xen 4.8
    
    xen.git commit 57f8b13c changed several of the libxl memory
    get/set functions to take 64 bit parameters. The libvirt
    libxl driver still uses uint32_t variables for these various
    parameters, which is particularly problematic for the
    libxl_set_memory_target() function.
    
    When dom0 autoballooning is enabled, libvirt (like xl) determines
    the memory needed to start a domain and the memory available. If
    memory available is less than memory needed, dom0 is ballooned
    down by passing a negative value to libxl_set_memory_target()
    'target_memkb' parameter. Prior to xen.git commit 57f8b13c,
    'target_memkb' was an int32_t. Subtracting a larger uint32 from
    a smaller uint32 and assigning it to int32 resulted in a negative
    number. After commit 57f8b13c, the same subtraction is widened
    to a int64, resulting in a large positive number. The simple
    fix taken by this patch is to assign the difference of the
    uint32 values to a temporary int32 variable, which is then
    passed to 'target_memkb' parameter of libxl_set_memory_target().
    
    Note that it is undesirable to change libvirt to use 64 bit
    variables since it requires setting LIBXL_API_VERSION to 0x040800.
    Currently libvirt supports LIBXL_API_VERSION >= 0x040400,
    essentially Xen >= 4.4.

Index: libvirt-3.0.0/src/libxl/libxl_domain.c
===================================================================
--- libvirt-3.0.0.orig/src/libxl/libxl_domain.c
+++ libvirt-3.0.0/src/libxl/libxl_domain.c
@@ -909,6 +909,7 @@ libxlDomainFreeMem(libxl_ctx *ctx, libxl
 {
     uint32_t needed_mem;
     uint32_t free_mem;
+    int32_t target_mem;
     int tries = 3;
     int wait_secs = 10;
 
@@ -922,7 +923,8 @@ libxlDomainFreeMem(libxl_ctx *ctx, libxl
         if (free_mem >= needed_mem)
             return 0;
 
-        if (libxl_set_memory_target(ctx, 0, free_mem - needed_mem,
+        target_mem = free_mem - needed_mem;
+        if (libxl_set_memory_target(ctx, 0, target_mem,
                                     /* relative */ 1, 0) < 0)
             goto error;