xen: balloon: allow PVMMU interfaces to be compiled out

The ARM platform has no concept of PVMMU and therefor no
HYPERVISOR_update_va_mapping et al. Allow this code to be compiled out
when not required.

In some similar situations (e.g. P2M) we have defined dummy functions
to avoid this, however I think we can/should draw the line at dummying
out actual hypercalls.
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/xen/Kconfig

@@ -6,6 +6,7 @@ config XEN
 	bool "Xen guest support"
 	select PARAVIRT
 	select PARAVIRT_CLOCK
+	select XEN_HAVE_PVMMU
 	depends on X86_64 || (X86_32 && X86_PAE && !X86_VISWS)
 	depends on X86_CMPXCHG && X86_TSC
 	help

drivers/xen/Kconfig

@@ -206,4 +206,7 @@ config XEN_MCE_LOG
 	  Allow kernel fetching MCE error from Xen platform and
 	  converting it into Linux mcelog format for mcelog tools
 
+config XEN_HAVE_PVMMU
+       bool
+
 endmenu

drivers/xen/balloon.c

@@ -359,6 +359,7 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
 
 		set_phys_to_machine(pfn, frame_list[i]);
 
+#ifdef CONFIG_XEN_HAVE_PVMMU
 		/* Link back into the page tables if not highmem. */
 		if (xen_pv_domain() && !PageHighMem(page)) {
 			int ret;
@@ -368,6 +369,7 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
 				0);
 			BUG_ON(ret);
 		}
+#endif
 
 		/* Relinquish the page back to the allocator. */
 		ClearPageReserved(page);
@@ -416,13 +418,14 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 
 		scrub_page(page);
 
+#ifdef CONFIG_XEN_HAVE_PVMMU
 		if (xen_pv_domain() && !PageHighMem(page)) {
 			ret = HYPERVISOR_update_va_mapping(
 				(unsigned long)__va(pfn << PAGE_SHIFT),
 				__pte_ma(0), 0);
 			BUG_ON(ret);
 		}
-
+#endif
 	}
 
 	/* Ensure that ballooned highmem pages don't have kmaps. */