xen: fixes and features for 5.1-rc1

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Merge tag 'for-linus-5.1a-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

Pull xen updates from Juergen Gross:
 "xen fixes and features:

   - remove fallback code for very old Xen hypervisors

   - three patches for fixing Xen dom0 boot regressions

   - an old patch for Xen PCI passthrough which was never applied for
     unknown reasons

   - some more minor fixes and cleanup patches"

* tag 'for-linus-5.1a-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  xen: fix dom0 boot on huge systems
  xen, cpu_hotplug: Prevent an out of bounds access
  xen: remove pre-xen3 fallback handlers
  xen/ACPI: Switch to bitmap_zalloc()
  x86/xen: dont add memory above max allowed allocation
  x86: respect memory size limiting via mem= parameter
  xen/gntdev: Check and release imported dma-bufs on close
  xen/gntdev: Do not destroy context while dma-bufs are in use
  xen/pciback: Don't disable PCI_COMMAND on PCI device reset.
  xen-scsiback: mark expected switch fall-through
  xen: mark expected switch fall-through

include/linux/memory_hotplug.h

@@ -100,6 +100,8 @@ extern void __online_page_free(struct page *page);
 
 extern int try_online_node(int nid);
 
+extern u64 max_mem_size;
+
 extern bool memhp_auto_online;
 /* If movable_node boot option specified */
 extern bool movable_node_enabled;