libxl: fix "xl mem-set" regression from 0c029c4da2

Said commit ("libxl_set_memory_target: retain the same maxmem offset on
top of the current target") caused a regression for "xl mem-set"
against Dom0: While prior to creation of the first domain this works,
the first domain creation involving ballooning breaks. Due to "enforce"
not being set in the domain creation case, and due to Dom0's initial
->max_pages (in the hypervisor) being UINT_MAX, the calculation of
"memorykb" in the first "xl mem-set" adusting the target upwards
subsequent to domain creation and termination may cause an overflow,
resulting in Dom0's maximum getting to a very small value. This small
maximum will the make the subsequent setting of the PoD target fail.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Note that this only fixes the immediate problem - there appear to be
further issues lurking here:
- libxl_set_memory_target()'s *_memkb variables all being 32-bit,
- libxl_domain_setmaxmem()'s max_memkb parameter being 32-bit,
- other similar code living elsewhere?
Note also that this requires
http://lists.xenproject.org/archives/html/xen-devel/2015-04/msg02485.html
(or some other change avoiding truncation) to also be in place in order
to address the observed problem.
Note further that xc_domain_setmaxmem() is being used by upstream qemu
and hence the libxc interface change here may represent a compatibility
issue.
Finally the setting of a PoD target for non-HVM domains seems bogus too
(even if it's expected to just be a no-op in that case).

--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -1256,7 +1256,7 @@ int xc_getcpuinfo(xc_interface *xch, int
 
 int xc_domain_setmaxmem(xc_interface *xch,
                         uint32_t domid,
-                        unsigned int max_memkb);
+                        uint64_t max_memkb);
 
 int xc_domain_set_memmap_limit(xc_interface *xch,
                                uint32_t domid,
--- a/tools/libxc/xc_domain.c
+++ b/tools/libxc/xc_domain.c
@@ -634,7 +634,7 @@ int xc_shadow_control(xc_interface *xch,
 
 int xc_domain_setmaxmem(xc_interface *xch,
                         uint32_t domid,
-                        unsigned int max_memkb)
+                        uint64_t max_memkb)
 {
     DECLARE_DOMCTL;
     domctl.cmd = XEN_DOMCTL_max_mem;
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -4726,7 +4726,8 @@ int libxl_set_memory_target(libxl_ctx *c
 {
     GC_INIT(ctx);
     int rc = 1, abort_transaction = 0;
-    uint32_t memorykb = 0, videoram = 0;
+    uint64_t memorykb;
+    uint32_t videoram = 0;
     uint32_t current_target_memkb = 0, new_target_memkb = 0;
     uint32_t current_max_memkb = 0;
     char *memmax, *endptr, *videoram_s = NULL, *target = NULL;
@@ -4820,7 +4821,7 @@ retry_transaction:
         rc = xc_domain_setmaxmem(ctx->xch, domid, memorykb);
         if (rc != 0) {
             LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR,
-                    "xc_domain_setmaxmem domid=%d memkb=%d failed "
+                    "xc_domain_setmaxmem domid=%u memkb=%"PRIu64" failed "
                     "rc=%d\n", domid, memorykb, rc);
             abort_transaction = 1;
             goto out;