Merge tag 'stable/for-linus-3.12-rc0-tag-three' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

Pull Xen balloon driver bug-fixes from Stefano Stabellini:
 - fix a preemption bug in xen/balloon.c;
 - remove an harmful BUG_ON in xen/balloon.c that can trigger in
   non-erroneous situations.

* tag 'stable/for-linus-3.12-rc0-tag-three' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  xen/balloon: remove BUG_ON in increase_reservation
  xen/balloon: ensure preemption is disabled when using a scratch page

drivers/xen/balloon.c

@@ -349,8 +349,6 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
 		BUG_ON(page == NULL);
 
 		pfn = page_to_pfn(page);
-		BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
-		       phys_to_machine_mapping_valid(pfn));
 
 		set_phys_to_machine(pfn, frame_list[i]);
 
@@ -380,6 +378,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 	enum bp_state state = BP_DONE;
 	unsigned long  pfn, i;
 	struct page   *page;
+	struct page   *scratch_page;
 	int ret;
 	struct xen_memory_reservation reservation = {
 		.address_bits = 0,
@@ -399,6 +398,8 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 	if (nr_pages > ARRAY_SIZE(frame_list))
 		nr_pages = ARRAY_SIZE(frame_list);
 
+	scratch_page = get_balloon_scratch_page();
+
 	for (i = 0; i < nr_pages; i++) {
 		page = alloc_page(gfp);
 		if (page == NULL) {
@@ -416,7 +417,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 		if (xen_pv_domain() && !PageHighMem(page)) {
 			ret = HYPERVISOR_update_va_mapping(
 				(unsigned long)__va(pfn << PAGE_SHIFT),
-				pfn_pte(page_to_pfn(__get_cpu_var(balloon_scratch_page)),
+				pfn_pte(page_to_pfn(scratch_page),
 					PAGE_KERNEL_RO), 0);
 			BUG_ON(ret);
 		}
@@ -432,14 +433,14 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 		pfn = mfn_to_pfn(frame_list[i]);
 		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 			unsigned long p;
-			struct page *pg;
-			pg = __get_cpu_var(balloon_scratch_page);
-			p = page_to_pfn(pg);
+			p = page_to_pfn(scratch_page);
 			__set_phys_to_machine(pfn, pfn_to_mfn(p));
 		}
 		balloon_append(pfn_to_page(pfn));
 	}
 
+	put_balloon_scratch_page();
+
 	set_xen_guest_handle(reservation.extent_start, frame_list);
 	reservation.nr_extents   = nr_pages;
 	ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);